-----BEGIN PRIVACY-ENHANCED MESSAGE----- Proc-Type: 2001,MIC-CLEAR Originator-Name: webmaster@www.sec.gov Originator-Key-Asymmetric: MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB MIC-Info: RSA-MD5,RSA, WVa+HDJJiZtcJI7A7C3QbmPrj8OVFuOoG9fhnILfUeQAvefz/BgEniCIsJJT7i/i 0bS+Ib0y/fL9M8b6qDTJ3g== 0000912057-02-038133.txt : 20021010 0000912057-02-038133.hdr.sgml : 20021010 20021009180144 ACCESSION NUMBER: 0000912057-02-038133 CONFORMED SUBMISSION TYPE: S-4 PUBLIC DOCUMENT COUNT: 11 FILED AS OF DATE: 20021010 FILER: COMPANY DATA: COMPANY CONFORMED NAME: AON CORP CENTRAL INDEX KEY: 0000315293 STANDARD INDUSTRIAL CLASSIFICATION: ACCIDENT & HEALTH INSURANCE [6321] IRS NUMBER: 363051915 STATE OF INCORPORATION: DE FISCAL YEAR END: 1231 FILING VALUES: FORM TYPE: S-4 SEC ACT: 1933 Act SEC FILE NUMBER: 333-100464 FILM NUMBER: 02785744 BUSINESS ADDRESS: STREET 1: 123 N WACKER DR CITY: CHICAGO STATE: IL ZIP: 60606 BUSINESS PHONE: 3127013000 FORMER COMPANY: FORMER CONFORMED NAME: COMBINED INTERNATIONAL CORP DATE OF NAME CHANGE: 19870504 S-4 1 a2086409zs-4.htm FORM S-4
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As filed with the Securities and Exchange Commission on October 10, 2002

Registration No. 333-

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM S-4
Registration Statement under the Securities Act of 1933

Aon CORPORATION
(Exact Name of Registrant as Specified in its Charter)

Delaware
(State or Other Jurisdiction
of Incorporation or Organization)

6321
(Primary Standard Industrial
Classification Code Number)

36-3051915
(I.R.S. Employer
Identification Number)

200 East Randolph Street
Chicago, Illinois 60601
(312) 381-1000
(Address, including zip code, and telephone number,
including area code, of Registrant's principal executive offices)

Raymond I. Skilling
Executive Vice President and Chief Counsel
Aon Corporation
200 East Randolph Street
Chicago, Illinois 60601
(312) 381-1000
(Name, address, including zip code, and telephone number,
including area code, of agent for service)

Copy of communications to:
Paul L. Choi
Frederick C. Lowinger
Sidley Austin Brown & Wood
Bank One Plaza
10 South Dearborn Street
Chicago, Illinois 60603
(312) 853-7000

Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this Registration Statement.

If the securities being registered on this form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box. o

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

CALCULATION OF REGISTRATION FEE

Title Of Each Class Of Securities To Be Registered	Amount To Be Registered	Proposed Maximum Offering Price Per Unit (1)	Proposed Maximum Aggregate Offering Price (1)	Amount Of Registration Fee


6.20% Notes due 2007	$250,000,000	100%	$250,000,000	$23,000

(1): Estimated solely for the purpose of calculating the registration fee pursuant to Rule 457(o) under the Securities Act of 1933, as amended.

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, or until the Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Subject To Completion, Dated October 9, 2002

PROSPECTUS

Aon Corporation

Offer to Exchange Up to $250,000,000 Aggregate Principal Amount of Our 6.20% Notes due 2007 for Any and All of the $250,000,000 Aggregate Principal Amount of Our Outstanding 6.20% Notes due 2007

The registered exchange offer will expire at 5:00 p.m., New York City time, on , 2002, unless extended.

We are offering to exchange up to $250,000,000 aggregate principal amount of our 6.20% notes due 2007 (which we refer to as the exchange notes) for $250,000,000 aggregate principal amount of our outstanding 6.20% notes due 2007 (which we refer to as the original notes). We sometimes refer to the exchange notes and the original notes collectively as the notes.

The terms of the exchange notes are substantially identical in all respects (including principal amount, interest rate and maturity) to the terms of the original notes for which they may be exchanged pursuant to this exchange offer, except that the exchange notes will be freely transferable by the holders (other than as described in this prospectus), are issued free of any covenant restricting transfer absent registration and will not have the right to earn additional interest arising from the failure to register the exchange notes. The exchange notes will evidence the same debt as the original notes. Original notes that are accepted for exchange will be canceled and retired. For a description of the terms of the notes, see "Description of the Notes." Aon Corporation will not receive any cash proceeds from this exchange offer.

Interest on the exchange notes will accrue at an initial rate per annum of 6.20%, subject to adjustment as described in this prospectus, from the most recent date to which interest has been paid on the original notes and will be payable semiannually in arrears on January 15 and July 15 of each year. Holders whose original notes are accepted for exchange will not receive any payment in respect of interest on the original notes for which the record date occurs on or after completion of the exchange offer. See "The Exchange Offer—Terms of the Exchange Offer."

The original notes were sold on December 13, 2001 in a transaction that was not registered under the Securities Act of 1933. Accordingly, the original notes may not be offered or sold within the United States or to, or for the account or benefit of, U.S. persons, except (1) to qualified institutional buyers under Rule 144A, (2) under certain circumstances, to institutional accredited investors or (3) outside the United States in compliance with Regulation S. We are offering the exchange notes to satisfy our obligations under the registration rights agreement relating to the original notes. See "The Exchange Offer—Purposes and Effects of the Exchange Offer."

The notes are not listed and will not be listed on any national securities exchange.

For a discussion of certain factors that you should consider before participating in this exchange offer, see "Risk Factors" beginning on page 10 of this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined that this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is , 2002.

TABLE OF CONTENTS

		Page
Summary		3
Risk Factors		10
Special Note on Forward-Looking Statements		12
Use of Proceeds		13
Ratios of Earnings to Fixed Charges		13
The Exchange Offer		14
Description of the Notes		23
Exchange Offer and Registration Rights		32
Certain U.S. Federal Income Tax Consequences		34
Plan of Distribution		36
Legal Matters		36
Experts		36
Where You Can Find More Information		37

This prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any notes offered hereby in any jurisdiction where, or to any person to whom, it is unlawful to make such offer or solicitation. The information contained in this prospectus speaks only as of the date of this prospectus unless the information specifically indicates that another date applies. No dealer, salesperson or other person has been authorized to give any information or to make any representations other than those contained or incorporated by reference in this prospectus in connection with the offer contained herein and, if given or made, such information or representations must not be relied upon as having been authorized by Aon Corporation. Neither the delivery of this prospectus nor any sale made hereunder shall under any circumstances create an implication that there has been no change in our affairs or that of our subsidiaries since the date hereof.

SUMMARY

This summary highlights selected information that we believe is especially important concerning Aon Corporation and the exchange offer and may not contain all of the information that may be important to you. You should read carefully this entire prospectus together with the documents incorporated by reference herein. Unless otherwise indicated, all references in this prospectus to "Aon," "we," "our," or "us" refer to Aon Corporation together with its subsidiaries.

Overview of Aon Corporation

We are a holding company whose operating subsidiaries carry on business in three distinct operating segments: (i) insurance brokerage and other services, (ii) consulting and (iii) insurance underwriting.

Our insurance brokerage and other services segment consists principally of our retail, reinsurance and wholesale brokerage, as well as related insurance services, including claims services, underwriting management, captive insurance company management services and premium financing. These services are provided by subsidiaries of Aon Group, Inc., and certain of our other indirect subsidiaries, including Aon Risk Services Companies, Inc.; Aon Holdings International bv; Aon Services Group, Inc.; Aon Re Worldwide, Inc.; Aon Limited (U.K.); Cananwill, Inc.; and Premier Auto Finance, Inc.

Our consulting segment provides a full range of human capital management services utilizing five practices: employee benefits, compensation, management consulting, outsourcing and communications. These services are provided primarily by subsidiaries and affiliates of Aon Consulting Worldwide, Inc., which is also a subsidiary of Aon Group.

Our insurance underwriting segment is comprised of supplemental accident and health and life insurance and extended warranty and casualty insurance products and services. Combined Insurance Company of America engages in the marketing and underwriting of accident and health and life insurance products. Combined Specialty Insurance Company (formerly known as Virginia Surety Company, Inc.) and London General Insurance Company Limited offer extended warranty and casualty insurance products and services.

We have 550 offices in over 125 countries and sovereignties and nearly 53,000 professionals and employees who serve millions of clients, policyholders and warrantyholders.

The mailing address of our principal executive offices is 200 East Randolph Street, Chicago, Illinois 60601, and the telephone number of our principal executive offices is (312) 381-1000.

The Exchange Offer

Purpose of Exchange		We sold the original notes in a private offering to qualified institutional buyers through Morgan Stanley & Co. Incorporated (the "initial purchaser"). In connection with that offering, we and the initial purchaser entered into a registration rights agreement dated as of December 13, 2001 (the "registration rights agreement") for the benefit of the holders of the original notes providing for, among other things, the exchange offer. The exchange offer is intended to make the exchange notes freely transferable by the holders without further registration or any prospectus delivery requirements under the Securities Act. See "The Exchange Offer—Purposes and Effects of the Exchange Offer."
The Exchange Offer		We are offering to exchange, pursuant to the exchange offer, up to $250 million aggregate principal amount of our new 6.20% notes due 2007 (the "exchange notes") for $250 million aggregate principal amount of our outstanding 6.20% notes due 2007 (the "original notes"). We sometimes refer to the exchange notes and the original notes collectively as the notes. The terms of the exchange notes and the original notes are identical in all material respects (including principal amount, interest rate and maturity), except that the exchange notes are freely transferable by the holders, are not subject to any covenant regarding registration under the Securities Act of 1933 and will not bear additional interest as a result of our failure to consummate the exchange offer under the terms of the registration rights agreement. See "The Exchange Offer—Terms of the Exchange Offer" and "—Procedures for Tendering." The exchange offer is not conditioned upon any minimum aggregate principal amount of original notes being tendered for exchange.
Expiration Date		The exchange offer will expire at 5:00 p.m., New York City time, on , 2002, unless extended (the "expiration date").
Conditions of the Exchange Offer		Our obligation to consummate the exchange offer is not subject to any conditions, other than that the exchange offer does not violate any applicable law or SEC staff interpretation. See "The Exchange Offer—Conditions of the Exchange Offer." We reserve the right to terminate or amend the exchange offer at any time prior to the expiration date if, among other things, there shall have been proposed, adopted or enacted any law, statute, rule, regulation or SEC staff interpretation which, in our judgment, could reasonably be expected to materially impair our ability to proceed with the exchange offer.

Procedures for Tendering Original Notes	Brokers, dealers, commercial banks, trust companies and other nominees who hold original notes through The Depository Trust Company ("DTC") may effect tenders by book-entry transfer in accordance with DTC's Automated Tender Offer Program ("ATOP"). To tender original notes for exchange by book-entry transfer, an agent's message (as defined under "The Exchange Offer—Procedures for Tendering") or a completed and signed letter of transmittal (or facsimile thereof), with any required signature guarantees and any other required documentation, must be delivered to the exchange agent at the address set forth in this prospectus on or prior to the expiration date, and the original notes must be tendered in accordance with DTC's ATOP procedures for transfer. To tender original notes for exchange by means other than book-entry transfer, you must complete, sign and date the letter of transmittal (or facsimile thereof) in accordance with the instructions in this prospectus and contained in the letter of transmittal and mail or otherwise deliver the letter of transmittal (or facsimile thereof), together with the original notes, any required signature guarantees and any other required documentation, to the exchange agent at the address set forth in this prospectus on or prior to the expiration date. By executing the letter of transmittal, you represent to us that:
	•	you are acquiring the exchange notes in the ordinary course of business;
	•	you are not engaged in, and do not intend to engage in, and have no arrangement or understanding with any person to participate in, the distribution of the original notes or the exchange notes within the meaning of the Securities Act;
	•	you are not an "affiliate" of Aon (as defined under the Securities Act) or, if you are an affiliate, that you will comply with the registration and prospectus delivery requirements of the Securities Act to the extent applicable; and
	•	you are not a broker-dealer who is acquiring exchange notes for original notes acquired for your own account as a result of market-making or other trading activities.
	See "The Exchange Offer—Procedures for Tendering."

Special Procedures for Beneficial Owners		If you are a beneficial owner whose original notes are registered in the name of a broker, dealer, commercial bank, trust company or other nominee and you wish to tender, you should contact the registered holder promptly and instruct the registered holder to tender on your behalf. If the original notes are in certificated form and you are a beneficial owner who wishes to tender on the registered holder's behalf, prior to completing and executing the letter of transmittal and delivering the original notes, you must either make appropriate arrangements to register ownership of the original notes in your name or obtain a properly completed bond power from the registered holder. The transfer of registered ownership may take considerable time. See "The Exchange Offer—Procedures for Tendering."
Guaranteed Delivery Procedures		If you wish to tender your original notes in the exchange offer but your original notes are not immediately available for delivery or other documentation cannot be completed by the expiration date, or the procedures for book-entry transfer cannot be completed on a timely basis, you may still tender your original notes by completing, signing and delivering the letter of transmittal or, in the case of a book-entry transfer, an agent's message, with any required signature guarantees and any other documents required by the letter of transmittal, to the exchange agent prior to the expiration date and tendering your original notes according to the guaranteed delivery procedures set forth in "The Exchange Offer—Guaranteed Delivery Procedures."
Withdrawal Rights		You may withdraw your tender of original notes at any time prior to 5:00 p.m., New York City time, on the expiration date. See "The Exchange Offer—Withdrawal of Tenders."
Acceptance of Original Notes and Delivery of Exchange Notes		Subject to the satisfaction or waiver of the conditions to the exchange offer, we will accept for exchange any and all original notes that are properly tendered to the exchange agent prior to 5:00 p.m., New York City time, on the expiration date. The exchange notes issued pursuant to the exchange offer will be delivered promptly following the expiration date. See "The Exchange Offer—Terms of the Exchange Offer."
Exchange Agent		The Bank of New York is serving as the exchange agent in connection with the exchange offer. See "The Exchange Offer—Exchange Agent."
Tax Consequences		For a summary of certain U.S. federal income tax consequences of ownership of the notes, the exchange of original notes for exchange notes and the disposition of notes, see "Certain U.S. Federal Income Tax Consequences."

Effect on Holders of the Original Notes		As a result of making this exchange offer, and upon acceptance for exchange of all validly tendered original notes pursuant to the terms thereof, we will have fulfilled some of our obligations under the registration rights agreement. However, because we did not fulfill these obligations on or prior to September 9, 2002 (the date that was 270 days after the closing of the sale of the original notes), the annual interest rate on the original notes was increased by 0.5% thereafter until consummation of the exchange offer or the effectiveness of a shelf registration statement covering resales of original notes. Accordingly, holders of original notes will receive additional interest during the period from September 10, 2002 until the date on which we consummate the exchange offer or cause a shelf registration statement covering resales of original notes to become effective, at which time the annual interest rate on the original notes will be decreased by 0.5%. Holders of original notes who do not tender their original notes will continue to be entitled to all of the rights and will be bound by all of the limitations applicable thereto under the indenture dated as of December 13, 2001 (the "indenture") between Aon and The Bank of New York, as trustee (the "trustee"), relating to the notes, except for any rights under the indenture or the registration rights agreement which by their terms terminate or cease to be effective as a result of our making and accepting for exchange all validly tendered original notes pursuant to the exchange offer (including the right to receive additional interest as described above). All original notes that remain outstanding will continue to be subject to the restrictions on transfer provided for in the original notes and the indenture. To the extent that original notes are tendered and accepted in the exchange offer, the trading market, if any, for original notes could be adversely affected.
Use of Proceeds		We will not receive any cash proceeds from the issuance of exchange notes pursuant to the exchange offer. We used the approximately $248.6 million net proceeds from the sale of the original notes to repay a portion of our outstanding commercial paper. See "Use of Proceeds."

Please review the information set forth under the heading "The Exchange Offer" beginning on page 14 for more detailed information concerning the exchange offer.

Terms of the Notes

The exchange offer applies to the entire $250 million aggregate principal amount of original notes that are outstanding. The terms of the original notes and exchange notes are identical in all material respects, except for certain transfer restrictions and registration and other rights relating to the exchange of the original notes for exchange notes. The exchange notes will evidence the same debt as the original notes and will be governed by the same indenture under which the original notes were issued. See "Description of the Notes."

Securities offered		$250,000,000 aggregate principal amount of 6.20% notes due 2007.
Issuer		Aon Corporation, a Delaware corporation.
Maturity Date		January 15, 2007.
Interest Payment Dates		January 15 and July 15 of each year.
Sinking Fund		None.
Ranking		The original notes are, and the exchange notes will be, our unsecured and unsubordinated obligations and will rank equally with all of our existing and future senior unsecured debt.
Interest Rate Adjustment		The interest rate payable on the notes will be subject to adjustment from time to time if either Moody's Investors Service or Standard & Poor's Rating Services lowers the rating ascribed to our senior unsecured debt below A3 in the case of Moody's or below A- in the case of Standard & Poor's. On August 7, 2002, Moody's lowered the rating ascribed to our senior unsecured debt to Baa1. As a result, the interest rate payable on the notes will be increased by 0.25%, commencing on January 15, 2003, subject to further increase or decrease in accordance with the terms of the indenture.
Covenants		The indenture contains a covenant limiting our ability to create liens on the present or future common stock of any of our significant subsidiaries.
Transfer Restrictions		The original notes have not been registered under the Securities Act and are subject to restrictions on transfer. The exchange notes have been registered under the Securities Act and are not subject to those restrictions.

Exchange Offer; Registration Rights		In the registration rights agreement, we agreed to file with the SEC one or more registration statements with respect to an offer to exchange the original notes for substantially similar notes that are registered under the Securities Act. Alternatively, if the exchange offer cannot be completed, we may file one or more shelf registration statements to cover resales of the original notes. Because we did not fulfill our obligations under the registration rights agreement on or prior to September 9, 2002 (the date that was 270 days after the closing of the sale of the original notes), the annual interest rate on the original notes was increased by 0.5% thereafter until consummation of the exchange offer or the effectiveness of a shelf registration statement covering resales of original notes. Accordingly, holders of original notes will receive additional interest during the period from September 10, 2002 until the date on which we consummate the exchange offer or cause a shelf registration statement covering resales of original notes to become effective, at which time the annual interest rate on the original notes will be decreased by 0.5%. This offering of exchange notes is being made to satisfy our obligations under the registration rights agreement.
No Public Market		The original notes are, and the exchange notes will be, a new issue of securities and will not be listed on any securities exchange or included in any automated quotation system. The initial purchaser has advised us that it intends to make a market in the original notes and, if issued, the exchange notes, but it is not obligated to do so and may discontinue its market-making activities at any time without notice.

RISK FACTORS

An investment in the notes involves risks. You should consider carefully the information set forth in this section and all the other information provided to you or incorporated by reference in this prospectus before deciding whether to exchange your original notes for exchange notes.

Risk Factors Relating to the Exchange Offer

You must carefully follow the required procedures in order to exchange your original notes.

The exchange notes will be issued in exchange for original notes only after timely receipt by the exchange agent of a duly executed letter of transmittal and all other required documents. Therefore, if you wish to tender your original notes, you must allow sufficient time to ensure timely delivery. Neither we nor the exchange agent has any duty to notify you of defects or irregularities with respect to tenders of original notes for exchange. Any holder of original notes who tenders in the exchange offer for the purpose of participating in a distribution of the exchange notes will be required to comply with the registration and prospectus delivery requirements of the Securities Act in connection with any resale transaction.

If you do not exchange original notes for exchange notes, transfer restrictions will continue and trading of the original notes may be adversely affected.

The original notes have not been registered under the Securities Act and are subject to substantial restrictions on transfer. Original notes that are not tendered for exchange or are tendered but are not accepted will, following completion of the exchange offer, continue to be subject to existing restrictions upon transfers. We do not currently expect to register the original notes under the Securities Act. To the extent that original notes are tendered and accepted in the exchange offer, the trading market for original notes, if any, could be adversely affected. See "The Exchange Offer—Consequences of Failure to Exchange."

Risk Factors Relating to an Investment in the Notes

We are a holding company and, therefore, may not be able to receive dividends in amounts needed to meet our obligations on the notes.

Our principal assets are the shares of capital stock of our subsidiaries, including our insurance underwriting companies. We rely on dividends from these subsidiaries to meet our obligations for paying principal and interest on outstanding debt obligations, including the notes, and for other corporate expenses. Payments from our underwriting subsidiaries are limited by governmental regulation and will depend on the surplus and future earnings of these subsidiaries. In some circumstances, specific payments from our insurance underwriting subsidiaries may require prior regulatory approval. We may not be able to receive dividends from these subsidiaries at times and in amounts we had anticipated, which may impact our ability to pay principal and interest on the notes when due.

The notes are effectively subordinated to the obligations of our subsidiaries.

Because we are a holding company, the holders of notes may not receive assets of our subsidiaries in a liquidation or recapitalization until the claims of our subsidiaries' creditors and insurance policyholders (in the case of insurance subsidiaries) are paid, except to the extent that we may have recognized claims against such subsidiaries.

The original notes are subject to restrictions on transfer.

We relied on an exemption from the registration requirements of the Securities Act and applicable state securities laws in offering the original notes. Accordingly, the original notes may be transferred or resold only in transactions registered, or exempt from registration, under the Securities Act and applicable state securities laws. The exchange of the original notes for exchange notes has been registered under the Securities Act.

Investors may find it difficult to trade the notes.

There is currently no public market for the original notes. The exchange notes are a new issue of securities with no established trading market. We do not intend to apply for listing of the notes on any securities exchange or for inclusion in any automated quotation system. Although the initial purchaser has informed us that it intends to make a market in the original notes and, if issued, the exchange notes, it is under no obligation to do so and may discontinue any market-making activities at any time without notice. Any such market-making will be subject to the limitations imposed by the Securities Act and the Exchange Act and may be limited during the exchange offer.

We cannot assure you that you will be able to sell your original notes or exchange notes at a particular time or that the prices that you receive when you sell will be favorable. We also cannot assure you as to the level of liquidity of the trading market for the exchange notes or, in the case of any holders of original notes that do not participate in the exchange offer, the trading market for the original notes. Future trading prices of the original notes and exchange notes will depend on many factors, including:

•: our operating performance and financial condition;
•: our ability to complete the offer to exchange the original notes for the exchange notes;
•: the interest of securities dealers in making a market for the original notes and the exchange notes; and
•: the market for similar securities.

SPECIAL NOTE ON FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated or deemed to be incorporated by reference herein contain statements concerning our future results and performance and other matters that are "forward-looking" statements within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934. The words "anticipates," "believes," "estimates," "expects," "plans," "intends" and similar expressions are intended, but are not the exclusive means, to identify these forward-looking statements. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from historical or anticipated results, depending on a variety of factors. Potential factors that could impact results include:

•: general economic conditions in different countries around the world;
•: fluctuations in global equity and fixed income markets;
•: changes in commercial property and casualty premium rates;
•: the competitive environment;
•: the actual cost of resolution of contingent liabilities and other loss contingencies;
•: the final execution of our business transformation plan, the ultimate cost and timing of our implementation thereof and the actual cost savings and other benefits resulting therefrom;
•: whether we ultimately dispose of some or all of our underwriting operations and the terms and timing thereof;
•: rating agency actions;
•: the cost and availability of debt and other financing; and
•: the events surrounding the terrorist attacks of September 11, 2001, including the timing and resolution of related insurance and reinsurance issues.

In light of these risks, uncertainties and assumptions, the forward-looking events discussed in this prospectus or documents incorporated or deemed to be incorporated by reference herein might not occur. We will not update forward-looking statements even though our situation may change in the future.

USE OF PROCEEDS

The exchange offer is intended to satisfy certain agreements we made with the initial purchaser of the original notes. We will not receive any cash proceeds from the issuance of the exchange notes offered by this prospectus. In consideration for issuing the exchange notes contemplated by this prospectus, we will receive the original notes in like principal amount, the form and terms of which are substantially the same as the form and term of the exchange notes (which replace the original notes, except as otherwise described in this prospectus, and which represent the same indebtedness). The original notes surrendered in exchange for the exchange notes will be retired and canceled and cannot be reissued. Accordingly, the issuance of the exchange notes will not result in any increase or decrease in our indebtedness.

We received approximately $248.6 million of net proceeds from the offering of the original notes (after deducting underwriting discounts and offering expenses). We received approximately $149.8 million of additional net proceeds from our concurrent offering of floating rate notes due 2003. We used all of the net proceeds from these offerings to repay a portion of our outstanding commercial paper.

RATIOS OF EARNINGS TO FIXED CHARGES

The following table presents the ratios of earnings to fixed charges for Aon and its consolidated subsidiaries for the periods indicated.

		Six Months Ended June 30,				Year Ended December 31,
		2002		2001		2001		2000		1999		1998		1997
Ratio of earnings to fixed charges		3.7x		1.9x		2.3x		4.2x		3.7x		5.4x		4.3x

For the purpose of calculating the ratios of earnings to fixed charges, earnings consist of income from continuing operations before provision for income taxes and minority interests and before fixed charges. Fixed charges include interest expense, interest credited on investment-type contracts and that portion of rental expense we deem to represent interest.

THE EXCHANGE OFFER

Purposes and Effects of the Exchange Offer

We sold the original notes on December 13, 2001 to the initial purchaser, who resold the original notes to "qualified institutional buyers" (as defined in Rule 144A under the Securities Act) in a private offering. In the registration rights agreement we agreed to file with the SEC a registration statement (the "exchange registration statement") with respect to an offer to exchange the original notes for exchange notes and to effect the exchange offer within 270 days following the sale of the original notes. A copy of the registration rights agreement has been filed as an exhibit to the registration statement of which this prospectus is a part.

This prospectus is a part of the exchange registration statement that we have filed with the SEC. The exchange offer is being made pursuant to the registration rights agreement to satisfy our obligations under that agreement. You are a "holder" with respect to the exchange offer if your original notes are registered in your name on our books or if you have obtained a properly completed bond power from the registered holder or any person whose original notes are held of record by DTC. Upon completion of the exchange offer, we will not be required to file any registration statement to register any outstanding original notes. If you do not tender your original notes, or if your original notes are tendered but not accepted, you generally will have to rely on exemptions to registration requirements under the securities laws, including the Securities Act, if you wish to sell your original notes.

Based on interpretations by the staff of the SEC set forth in no-action letters issued to third parties unrelated to Aon, we believe that you may offer for resale, resell or otherwise transfer the exchange notes issued to you, unless you are an "affiliate" of Aon within the meaning of Rule 405 under the Securities Act and except as set forth in the next paragraph, without compliance with the registration and prospectus delivery provisions of the Securities Act, provided that you acquire the exchange notes in the ordinary course of business and you are not engaged, do not intend to engage, and have no arrangement or understanding with any person to engage, in the distribution of the exchange notes. If you participate in the exchange offer for the purpose of distributing securities in a manner not permitted by the SEC's interpretation, the position of the staff of the SEC enunciated in the interpretive letters is inapplicable to you and you are required to comply with the registration and prospectus delivery requirements of the Securities Act in connection with any resale transaction. For this reason, broker-dealers may not participate in the exchange offer with respect to original notes acquired for their own accounts as a result of market-making or other trading activities.

The exchange offer is not being made to you, and you may not participate in the exchange offer, in any jurisdiction in which the exchange offer or its acceptance would not be in compliance with the securities laws of that jurisdiction. Prior to the exchange offer, however, we will use our reasonable best efforts to register or qualify the exchange notes for offer and sale under the securities laws of any jurisdictions necessary to permit completion of the exchange offer and do any and all other acts or things necessary or advisable to enable the offer and sale of the exchange notes in those jurisdictions.

Terms of the Exchange Offer

Upon the terms and subject to the conditions set forth in this prospectus and in the accompanying letter of transmittal, we will accept any and all original notes validly tendered prior to 5:00 p.m., New York City time, on the expiration date. You should read "—Expiration Date; Extension; Termination; Amendments" below for an explanation of how the expiration date may be extended. We will issue up to $250 million aggregate principal amount of exchange notes in exchange for a like principal amount of outstanding original notes that are validly tendered and accepted in the exchange offer. Subject to the conditions of the exchange offer described below, we will accept any and all original notes that are validly tendered. You may tender some or all of your original notes pursuant to the exchange offer.

The exchange offer is not conditioned upon any number or aggregate principal amount of original notes being tendered.

The form and terms of the exchange notes will be the same in all material respects as the form and terms of the original notes, except that the exchange notes will be registered under the Securities Act and hence will not bear legends restricting their transfer. The exchange notes will not represent additional indebtedness of Aon and will be entitled to the benefits of the indenture, which is the same indenture under which the original notes were issued. Original notes that are accepted for exchange will be cancelled and retired.

Interest on the exchange notes will accrue from the most recent date to which interest has been paid on the original notes. Accordingly, registered holders of exchange notes on the relevant record date for the first interest payment date following the completion of the exchange offer will receive interest accruing from the most recent date to which interest has been paid. Original notes accepted for exchange will cease to accrue interest from and after the date the exchange offer closes. If your original notes are accepted for exchange, you will not receive any payment in respect of interest on the original notes for which the record date occurs on or after completion of the exchange offer.

You do not have any appraisal or dissenters' rights under the indenture in connection with the exchange offer. We intend to conduct the exchange offer in accordance with the provisions of the registration rights agreement. If you do not tender for exchange or if your tender is not accepted, the original notes will remain outstanding and you will be entitled to the benefits of the indenture, but will not be entitled to any registration rights under the registration rights agreement.

We will be deemed to have accepted validly tendered original notes when, as and if we have given oral or written notice of acceptance to the exchange agent for the exchange offer. The exchange agent will act as agent for the tendering holders for the purpose of receiving the exchange notes from us.

If any tendered original notes are not accepted for exchange because of an invalid tender, the occurrence of certain other events set forth in this prospectus or otherwise, we will return the certificates (if any) for the unaccepted original notes to the tendering holders of those notes, without expense, as promptly as practicable after the expiration date.

If you tender your original notes in the exchange offer, you will not be required to pay brokerage commissions or fees or, subject to the instructions in the letter of transmittal, transfer taxes with respect to the exchange of original notes pursuant to the exchange offer. We will pay all charges and expenses, other than certain applicable taxes described below, in connection with the exchange offer. See "Fees and Expenses" below.

Conditions of the Exchange Offer

Our obligation to consummate the exchange offer is not subject to any conditions, other than that the exchange offer does not violate any applicable law or SEC staff interpretation. Accordingly, we will not be required to accept for exchange any original notes tendered and may terminate or amend the exchange offer as provided herein before the acceptance of any original notes if:

•: any action or proceeding is instituted or threatened in any court or by or before any governmental agency or regulatory authority with respect to the exchange offer which, in our judgment, could reasonably be expected to materially impair our ability to proceed with the exchange offer; or
•: there shall have been proposed, adopted or enacted any law, statute, rule, regulation, order or SEC staff interpretation which, in our judgment, could reasonably be expected to materially impair our ability to proceed with the exchange offer.

The foregoing conditions are for our sole benefit and may be asserted by us regardless of the circumstances giving rise to any of these conditions or may be waived by us in whole or in part at any time and from time to time in our sole discretion. Our failure to exercise any of the foregoing rights at

any time is not a waiver of any of these rights, and each of these rights will be an ongoing right which may be asserted at any time and from time to time. If we waive or amend the foregoing conditions, we will, if required by applicable law, extend the exchange offer for a minimum of five business days from the date that we first give notice, by public announcement or otherwise, of such waiver or amendment, if the exchange offer would otherwise expire within that five business-day period. Our determination concerning the events described above will be final and binding upon all parties.

Expiration Date; Extension; Termination; Amendments

The exchange offer will expire at 5:00 p.m., New York City time, on , 2002, unless extended (the "expiration date"). We reserve the right to extend the exchange offer at our discretion, in which event the term "expiration date" shall mean the time and date on which the exchange offer as so extended shall expire. We will notify the exchange agent of any extension by oral or written notice and will make a public announcement to that effect, each prior to 9:00 a.m., New York City time, on the next business day after the previously scheduled expiration date. We may also accept all properly tendered original notes as of the expiration date and extend the expiration date in respect of the remaining outstanding original notes. We reserve the right, in our sole discretion, to:

•: delay accepting for exchange any original notes for exchange notes or extend or terminate the exchange offer and not accept for exchange any original notes for exchange notes if any of the events set forth under the caption "Conditions of the Exchange Offer" occur and we do not waive the condition by giving oral or written notice of the delay or termination to the exchange agent; or
•: amend the terms of the exchange offer in any manner.

Any delay in acceptance for exchange, extension or amendment will be followed as promptly as practicable by a public announcement of the delay. If we amend the exchange offer in a manner we determine constitutes a material change, we will promptly disclose the amendment in a manner reasonably calculated to inform the holders of original notes of the amendment, and we will extend the exchange offer for a period of five to ten business days, depending upon the significance of the amendment and the manner of disclosure to the holders of the original notes, if the exchange offer would otherwise expire during that five to ten business day period. The rights we have reserved in this paragraph are in addition to our rights set forth under the caption "Conditions of the Exchange Offer."

Procedures For Tendering

Only a holder of original notes may tender them in the exchange offer. To validly tender in the exchange offer by book-entry transfer, you must deliver an agent's message or a completed and signed letter of transmittal (or facsimile thereof), together with any required signature guarantees and any other required documents, to the exchange agent prior to 5:00 p.m., New York City time, on the expiration date, and the original notes must be tendered pursuant to the procedures for book-entry transfer set forth below. To validly tender by means other than book-entry transfer, you must deliver a completed and signed letter of transmittal (or facsimile thereof), together with any required signature guarantees and any other required documents and the original notes, to the exchange agent prior to 5:00 p.m., New York City time, on the expiration date.

Any financial institution that is a participant in DTC's Book-Entry Transfer Facility system may make book-entry delivery of the original notes by causing DTC to transfer the original notes into the exchange agent's account in accordance with DTC's ATOP procedures for transfer. However, although delivery of original notes may be effected through book-entry transfer into the exchange agent's account at DTC, an agent's message or a completed and signed letter of transmittal (or facsimile thereof), with any required signature guarantees and any other required documents, must, in any case, be transmitted to and received or confirmed by the exchange agent at its addresses set forth under the caption "Exchange Agent" prior to 5:00 p.m., New York City time, on the expiration date, or the

guaranteed delivery procedure set forth below must be complied with. DELIVERY OF DOCUMENTS TO DTC IN ACCORDANCE WITH DTC'S PROCEDURES DOES NOT CONSTITUTE DELIVERY TO THE EXCHANGE AGENT.

The term "agent's message" means, with respect to any tendered original notes, a message transmitted by DTC to and received by the exchange agent and forming part of a book-entry confirmation, stating that DTC has received an express acknowledgment from each tendering participant to the effect that, with respect to those original notes, the participant has received and agrees to be bound by the letter of transmittal and that Aon may enforce the letter of transmittal against the participant. The term "book-entry confirmation" means a timely confirmation of a book-entry transfer of original notes into the exchange agent's account at DTC.

If you tender an original note, and do not validly withdraw your tender, your actions will constitute an agreement with us in accordance with the terms and subject to the conditions set forth in this prospectus and in the letter of transmittal.

The method of delivery of your original notes and the letter of transmittal and all other required documents to the exchange agent is at your election and risk. Instead of delivery by mail, we recommend that you use an overnight or hand delivery service. In all cases, you should allow sufficient time to assure delivery to the exchange agent before the expiration date. No letter of transmittal or original note should be sent to Aon; instead, they should be sent to the exchange agent. You may request that your broker, dealer, commercial bank, trust company or nominee effect the tender for you.

Signatures on a letter of transmittal or a notice of withdrawal, as the case may be, must be guaranteed by an eligible institution (as defined below) unless the original notes are being tendered:

•: by a registered holder who has not completed the box entitled "Special Issuance Instructions" or "Special Delivery Instructions" on the letter of transmittal; or
•: for the account of an eligible institution.

If signatures on a letter of transmittal or a notice of withdrawal, as the case may be, are required to be guaranteed, the guarantee must be by a member of a signature guarantee program within the meaning of Rule 17Ad-15 under the Exchange Act (an "eligible institution").

If the letter of transmittal or any original notes or bond powers are signed by trustees, executors, administrators, guardians, attorneys-in-fact, officers of corporations or others acting in a fiduciary or representative capacity, those persons should so indicate when signing, and unless we waive it, evidence satisfactory to us of their authority to act must be submitted with the letter of transmittal.

We will determine, in our sole discretion, all questions as to the validity, form, eligibility (including time of receipt) and acceptance and withdrawal of tendered original notes. Our determination will be final and binding. We reserve the absolute right to reject any and all original notes not properly tendered or any original notes our acceptance of which would, in the opinion of our counsel, be unlawful. We also reserve the right to waive any defects, irregularities or conditions of tender as to particular original notes. Our interpretation of the terms and conditions of the exchange offer (including the instructions in the letter of transmittal) will be final and binding on all parties.

Unless waived, you must cure any defects or irregularities in connection with tenders of your original notes within a time period we will determine. Although we intend to request that the exchange agent notify you of defects or irregularities with respect to your tender of original notes, we will not, nor will the exchange agent or any other person, incur any liability for failure to give you any notification. Tenders of original notes will not be deemed to have been made until any defects or irregularities have been cured or waived. Any original notes received by the exchange agent that are not properly tendered and as to which the defects or irregularities have not been cured or waived will be returned by the exchange agent to the tendering holders, unless otherwise provided in the letter of transmittal, as soon as practicable following the expiration date.

In addition, we reserve the right in our sole discretion (subject to the limitations contained in the indenture):

•: to purchase or make offers for any original notes that remain outstanding after the expiration date; and
•: to the extent permitted by applicable law, to purchase original notes in the open market, in privately negotiated transactions or otherwise.

The terms of any purchases or offers could differ from the terms of the exchange offer.

By tendering, you represent to us, among other things, that:

•: you are obtaining the exchange notes in the ordinary course of business whether or not you are the holder;
•: you do not have an arrangement or understanding with any person to participate in the distribution of the exchange notes;
•: you are not an "affiliate," as defined in Rule 405 under the Securities Act, of Aon or, if you are an affiliate of Aon, that you will comply with the registration and prospectus delivery requirements of the Securities Act, to the extent applicable; and
•: you are not a broker-dealer who is acquiring exchange notes for original notes acquired for your own account as a result of market-making or other trading activities.

Guaranteed Delivery Procedures

If you wish to tender your original notes and either your original notes are not immediately available, or you cannot deliver your original notes and other required documents to the exchange agent, or cannot complete the procedure for book-entry transfer prior to the expiration date, you may effect a tender if:

•: you make a tender through an eligible institution;
•: prior to the expiration date, the exchange agent receives from the eligible institution a properly completed and duly executed notice of guaranteed delivery (by facsimile transmission, mail or hand delivery) setting forth your name and address, the certificate number(s) of the original notes (if available) and the principal amount of original notes tendered together with a duly executed letter of transmittal (or a facsimile thereof), stating that the tender is being made thereby and guaranteeing that, within three business days after the expiration date, the certificate(s) representing the original notes to be tendered, in proper form for transfer (or a confirmation of a book-entry transfer into the exchange agent's account at DTC of original notes delivered electronically) and any other documents required by the letter of transmittal, will be deposited by the eligible institution with the exchange agent; and
•: the certificate(s) representing all tendered original notes in proper form for transfer (or confirmation of a book-entry transfer into the exchange agent's account at DTC of original notes delivered electronically) and all other documents required by the letter of transmittal are received by the exchange agent within three business days after the expiration date.

Upon request to the exchange agent, you will be sent a notice of guaranteed delivery if you wish to tender your original notes according to the guaranteed delivery procedures set forth above.

Withdrawal of Tenders

Except as otherwise provided in this prospectus, you may withdraw any tenders of original notes at any time prior to 5:00 p.m., New York City time, on the expiration date, unless previously accepted for exchange.

For your withdrawal to be effective, the exchange agent must receive a written or facsimile transmission notice of withdrawal at its address set forth herein prior to 5:00 p.m., New York City time, on the expiration date, and prior to acceptance for exchange by Aon. Any notice of withdrawal must:

•: specify the name of the person having tendered the original notes to be withdrawn;
•: identify the original notes to be withdrawn (including the certificate number or numbers, if applicable, and principal amount of the original notes);
•: be signed in the same manner as the original signature on the letter of transmittal by which the original notes were tendered (including any required signature guarantees) or be accompanied by documents of transfer sufficient to have the trustee with respect to the original notes register the transfer of the original notes into the name of the person withdrawing the tender; and
•: specify the name in which any original notes are to be registered, if different from that of the person having tendered the original notes.

We will determine all questions as to the validity, form and eligibility (including time of receipt) of withdrawal notices. This determination shall be final and binding on all parties. Any original notes so withdrawn will be deemed not to have been validly tendered for purposes of the exchange offer and no exchange notes will be issued with respect to them unless the original notes so withdrawn are validly re-tendered. Any original notes which have been tendered but which are not accepted for exchange or which are withdrawn will be returned to you, without cost, as soon as practicable after withdrawal, rejection of tender or termination of the exchange offer. You may re-tender properly withdrawn original notes by following one of the procedures described above under "Procedures for Tendering" at any time prior to the expiration date.

Fees and Expenses

We will bear the expenses of soliciting tenders pursuant to the exchange offer. The principal solicitation for tenders pursuant to the exchange offer is being made by mail; however, additional solicitation may be made by telegraph, telephone, telecopy, in person of by other means by our officers and regular employees and by officers and employees of our affiliates.

We have not retained any dealer-manager in connection with the exchange offer and will not make any payments to brokers, dealers or others soliciting acceptances of the exchange offer. However, we will pay the exchange agent reasonable and customary fees for its services and will reimburse it for its reasonable out-of-pocket expenses. We may also pay brokerage houses and other custodians, nominees and fiduciaries the reasonable out-of-pocket expenses incurred by them in forwarding copies of this prospectus, letters of transmittal and related documents to the beneficial owners of the original notes and in handling or forwarding tenders for exchange. We will pay the other expenses incurred in connection with the exchange offer, including fees and expenses of the trustee, accounting and legal fees and printing costs.

We will pay all transfer taxes, if any, applicable to the exchange of original notes pursuant to the exchange offer. If, however, certificates representing exchange notes or original notes for principal amounts not tendered or accepted for exchange are to be delivered to, or are to be issued in the name of, any person other than the registered holder of the original notes tendered, or if tendered original notes are registered in the name of any person other than the person signing the letter of transmittal, or if a transfer tax is imposed for any reason other than the exchange of original notes pursuant to the

exchange offer, then the amount of any transfer taxes (whether imposed on the registered holder or any other persons) will be payable by the tendering holder. If satisfactory evidence of payment of any taxes or exemption therefrom is not submitted with the letter of transmittal, the amount of any transfer taxes will be billed directly to the tendering holder.

Resale of Exchange Notes

Based on an interpretation by the staff of the SEC set forth in no-action letters issued to third parties, we believe that, unless you are an affiliate of Aon, you may offer for resale, resell or otherwise transfer the exchange notes issued to you pursuant to the exchange offer without compliance with the registration and prospectus delivery provisions of the Securities Act, provided that you acquire the exchange notes in the ordinary course of business and you do not intend to participate and have no arrangement or understanding with any person to participate in the distribution of the exchange notes. If you are an affiliate of Aon or if you tender in the exchange offer with the intention to participate, or for the purpose of participating, in a distribution of the exchange notes, you may not rely on the position of the staff of the SEC enunciated in Exxon Capital Holdings Corporation (available May 13, 1988) and Morgan Stanley & Co., Incorporated (available June 5, 1991), or similar no-action letters, but rather must comply with the registration and prospectus delivery requirements of the Securities Act in connection with any resale transaction. In addition, any such resale transaction should be covered by an effective registration statement containing the selling security holders information required by Item 507 of Regulation S-K of the Securities Act.

By tendering in the exchange offer, you represent to us that, among other things:

•

you are obtaining the exchange notes in the ordinary course of business;

•

you do not have an arrangement or understanding with any person to participate in the distribution of the exchange notes;

•

you are not a broker-dealer who is acquiring exchange notes for original notes acquired for your own account as a result of market-making or other trading activities; and

•

you acknowledge that if you participate in the exchange offer for the purpose of distributing the exchange notes:

•: you must, in the absence of an exemption therefrom, comply with the registration and prospectus delivery requirements of the Securities Act in connection with any resale of the exchange notes and you cannot rely on the no-action letters described above; and
•: your failure to comply with those requirements could result in you incurring liability under the Securities Act for which you are not indemnified by us.

Further, if you are an "affiliate" (as defined under Rule 405 of the Securities Act) of Aon, by tendering in the exchange offer you will represent to us that you understand and acknowledge that the exchange notes may not be offered for resale, resold or otherwise transferred by you without registration under the Securities Act or an exemption from registration.

Consequences of Failure to Exchange

As a result of making of this exchange offer, we will have fulfilled one of our obligations under the registration rights agreement. You generally will not have any further registration rights under the registration rights agreement or otherwise if you do not tender your original notes. Accordingly, if you do not exchange your original notes for exchange notes, you will continue to hold your untendered original notes and will be entitled to all the rights and limitations applicable thereto under the indenture, except to the extent of those rights or limitations that, by their terms, terminate or cease to have further effectiveness as a result of the exchange offer (including the right to receive additional

interest as a result of our failure to consummate the exchange offer or to cause a registration statement covering resales of original notes to become effective on or prior to September 9, 2002, as described under "Exchange Offer and Registration Rights.")

The original notes that are not exchanged for exchange notes pursuant to the exchange offer will remain restricted securities. Accordingly, you may only resell the original notes:

•: to us;
•: pursuant to an effective registration statement under the Securities Act;
•: so long as the original notes are eligible for resale pursuant to Rule 144A, to a qualified institutional buyer within the meaning of Rule 144A under the Securities Act in a transaction meeting the requirements of Rule 144A;
•: outside the United States to a foreign person pursuant to the exemption from the registration requirements of the Securities Act provided by Regulation S under the Securities Act;
•: to an institutional accredited investor that, prior to such transfer, furnishes to the trustee a signed letter containing certain representations and agreements relating to the restrictions on transfer of the original notes (the form of which letter can be obtained from the trustee); or
•: pursuant to another available exemption from the registration requirements of the Securities Act;

in each case in accordance with any applicable securities laws of any state of the United States.

To the extent that any original notes are tendered and accepted in the exchange offer, the trading market, if any, for the untendered original notes could be adversely affected. See "Termination of Certain Rights."

Termination of Certain Rights

You will not be entitled to certain rights under the registration rights agreement following the completion of the exchange offer. The right that will terminate is the right to receive additional interest as a result of our failure to consummate the exchange offer or to cause a registration statement covering resales of original notes to become effective on or prior to September 9, 2002, as described under "Exchange Offer and Registration Rights."

Other

Participation in the exchange offer is voluntary and you should carefully consider whether to accept. You are urged to consult your financial and tax advisors in making your decision on what action to take.

No person has been authorized to give any information or to make any representations in connection with the exchange offer other than those contained in this prospectus. If given or made, that information or those representations should not be relied upon as having been authorized by us. Neither the delivery of this prospectus nor any exchange made pursuant to the exchange offer will, under any circumstances, create any implication that there has been no change in our affairs or those of our subsidiaries since the respective dates as of which the information contained in this prospectus is given. The exchange offer is not being made to (and tenders will not be accepted from or on behalf of) holders of original notes in any jurisdiction in which the making of the exchange offer or the acceptance thereof would not be in compliance with the laws of such jurisdiction. However, we intend to take any action we deem necessary to permit the completion of the exchange offer in any jurisdiction and to extend the exchange offer to holders of original notes in that jurisdiction.

We may in the future seek to acquire original notes in open market or privately negotiated transactions, through subsequent exchange offers or otherwise. We have no present plans to acquire any original notes that are not tendered in the exchange offer nor to file a registration statement to permit resales of any original notes.

Accounting Treatment

The exchange notes will be recorded at the same carrying value as the original notes, as reflected in our accounting records on the date of the exchange. Accordingly, we will not recognize any gain or loss for accounting purposes upon the completion of the exchange offer. The expenses of the exchange offer will be amortized over the term of the exchange notes under accounting principles generally accepted in the United States.

Exchange Agent

The Bank of New York has been appointed as exchange agent for the exchange offer. All correspondence in connection with the exchange offer and the letter of transmittal should be addressed to the exchange agent, as follows:

By Mail, Hand or Overnight Courier:		By Facsimile:
The Bank of New York Corporate Trust Reorganization Unit 101 Barclay 7 East New York, New York 10286		The Bank of New York Corporate Trust Reorganization Unit (212) 298-1915

For Information or Confirmation by Telephone:
(212) 815-6331

Requests for assistance or for additional copies of this prospectus or the letter of transmittal should be directed to the exchange agent.

DESCRIPTION OF THE NOTES

The original notes were, and the exchange notes will be, issued under an indenture dated as of December 13, 2001 between us and The Bank of New York, as trustee. The terms of the notes include those stated in the indenture and those made a part of the indenture by reference to the Trust Indenture Act of 1939, as amended.

The following summary of selected provisions of the indenture and the notes is not complete and is subject to, and is qualified in its entirety by reference to, all of the provisions of the indenture and the notes. Copies of the indenture and the forms of certificates evidencing the notes are available from us upon request.

In this section, references to "Aon," "we," "our" and "us" mean Aon Corporation excluding, unless the context otherwise requires or otherwise expressly stated, its subsidiaries. Capitalized terms that are used in the following summary but not defined have the meanings given to those terms in the indenture.

General

The original notes are, and the exchange notes will be, our unsecured and unsubordinated obligations, initially limited to $250 million in aggregate principal amount. The notes are not obligations of or guaranteed by any of our subsidiaries. Under the indenture we may, without the consent of the holders of the notes, issue additional notes from time to time in the future.

The notes will mature on January 15, 2007. Interest on the notes will accrue from the most recent date to which interest has been paid or duly provided for at an initial per annum rate of 6.20%, subject to adjustment as described below, and will be payable semiannually in arrears on January 15 and July 15 of each year. Interest on the notes will be payable to the persons in whose names the notes are registered at the close of business on the fifteenth calendar day, whether or not a business day, immediately preceding an interest payment date.

The notes will be issued in fully registered form without coupons in denominations of $1,000 and integral multiples of $1,000. The notes will be denominated and payable in U.S. dollars.

The original notes were, and the exchange notes will be, issued in book-entry form, evidenced by one or more registered global certificates without coupons, which we sometimes refer to as "global notes," registered in the name of The Depository Trust Company ("DTC") or its nominee. Holders of interests in global notes will not be entitled to receive notes in definitive certificated form registered in their names except in the limited circumstances described below and in the private offering memorandum under which the original notes were issued. See "—Global Notes; Book-Entry System" for a summary of selected provisions applicable to transfer or exchange of global notes.

Notes in certificated form may be presented for payment and surrendered for registration of transfer or exchange at our agency maintained for that purpose in the Borough of Manhattan, The City of New York, currently the office of the trustee located at 101 Barclay Street, Floor 21W, New York, New York 10286. Holders will not be required to pay any charge for the registration of transfer or exchange of notes, other than any tax or other governmental charge payable in connection with the transfer or exchange, but subject to the limitations provided in the indenture.

Payment of interest on global notes will be made to DTC or its nominee. Payment of interest on notes in certificated form will be made against presentation of those notes at the agency referred to in the preceding paragraph or, at our option, by mailing checks payable to the persons entitled to that interest to their addresses as they appear in the note register.

The notes are not entitled to the benefit of any sinking fund nor subject to repurchase by us at the option of the holders prior to maturity. Except to the limited extent described below under

"—Consolidation and Merger," the indenture does not contain any provisions that are intended to protect holders of notes in the event of a highly-leveraged or similar transaction affecting us. Except to the limited extent described below under "—Certain Restrictions—Limitation on Liens," the indenture also does not limit our ability or the ability of any of our subsidiaries to incur additional debt in the future.

Because we are a holding company, the holders of the notes may not receive assets of our subsidiaries in a liquidation or recapitalization until the claims of our subsidiaries' creditors and insurance policyholders (in the case of insurance subsidiaries) are paid, except to the extent that we may have recognized claims against such subsidiaries. In addition, certain regulatory laws limit some of our subsidiaries from making payments to us of dividends and on loans and other transfers of funds.

Interest

The notes will bear interest at an initial rate of 6.20% per annum, subject to adjustment as described below, which will be paid semiannually in arrears on January 15 and July 15 of each year. Each date of payment with respect to the notes is referred to as an "interest payment date." If any interest payment date or the maturity date for the notes falls on a day that is not a business day, the payment of principal and interest will be made on the next succeeding business day as if made on the date such payment was due, and no interest will accrue on such payment for the period from and after the interest payment date or the maturity date, as the case may be, to the date of such payment on the next succeeding business day.

Interest on the notes will accrue from, and including, the most recent interest payment date to which interest has been paid or duly provided for to, but excluding, the next interest payment date or the maturity date, as the case may be. Interest on the notes will be computed on the basis of a 360-day year consisting of twelve 30-day months.

We will pay the interest payable on any interest payment date to the persons in whose name the notes are registered at the close of business on the fifteenth calendar day, whether or not a business day, immediately preceding that interest payment date. However, we will pay interest on the maturity date to the persons to whom the principal will be payable.

When we use the term "business day," we mean any day except a Saturday, Sunday or legal holiday on which banking institutions in The City of New York are authorized or required by law, regulation or executive order to close.

Optional Redemption

The notes are not redeemable prior to their maturity date.

Interest Rate Adjustment

The interest rate payable on the original notes are, and the interest rate payable on the exchange notes will be, subject to adjustment from time to time if either Moody's Investors Service ("Moody's") or Standard & Poor's Rating Services ("S&P") reduces the rating ascribed to our senior unsecured debt below A3 in the case of Moody's or below A- in the case of S&P. In this event, the interest rate payable on the notes will be increased by 0.25% for each rating category downgrade by either rating agency below A3 or A-, as the case may be. In addition, if Moody's or S&P subsequently increases the rating ascribed to our senior unsecured debt, then the interest rate payable on the notes will be decreased by 0.25% for each rating category upgrade by either rating agency, but in no event will the interest rate payable on the notes be reduced to below its initial level. Any such interest rate increase or decrease will take effect commencing on the interest payment date next following the related rating downgrade or upgrade, as the case may be, and remain in effect during all subsequent interest periods,

subject to the further adjustments and limitations set forth in the immediately preceding sentence. For this purpose, a ratings category is the difference between a particular rating assigned by either Moody's or S&P and the next higher or lower rating. For example, in the case of Moody's the difference between Baa1 and Baa2 shall constitute one rating category, and in the case of S&P the difference between BBB+ and BBB shall constitute one rating category. There is no limit to the number of times the interest rate payable on the notes can be adjusted.

On August 7, 2002, Moody's lowered the rating ascribed to our senior unsecured debt to Baa1. As a result, the interest rate payable on the notes will be increased by 0.25%, commencing on January 15, 2003, subject to further increase or decrease in accordance with the terms of the indenture.

Certain Restrictions

The following restriction will apply to the notes.

Limitation on Liens

Under the indenture we have agreed, among other things, to not, directly or indirectly, create, issue, assume, incur or guarantee any indebtedness for money borrowed which is secured by a mortgage, pledge, lien, security interest or other encumbrance of any nature on any of the present or future common stock of any of our significant subsidiaries (or any company besides us having direct or indirect control of any of our significant subsidiaries). This restriction will not apply if we ensure that the notes (together with, if we decide, any other indebtedness for money borrowed by us then existing or thereafter created which is not subordinate to the notes) will be secured equally and proportionately with (or, at our option, prior to) such other secured indebtedness for as long as such indebtedness is secured.

For purposes of this restriction, "significant subsidiary" means any of our subsidiaries that constitutes a "significant subsidiary" as defined in Rule 1-02(w) of Regulation S-X under the Exchange Act.

Events of Default

An Event of Default with respect to the notes will occur under the indenture if:

•: we fail to pay the principal of the notes when due;
•: we fail to pay the interest on the notes when due and such failure continues for 30 days;
•: we fail to comply with any of our other agreements contained in the indenture and such failure continues for 90 days after written notice of that failure is given to us from the trustee (or to us and the trustee from the holders of at least 25% in principal amount of the outstanding notes); or
•: certain events of bankruptcy, insolvency or reorganization relating to us have occurred and are continuing.

If there is a continuing event of default with respect to the notes, the trustee or the holders of at least 25% in principal amount of the outstanding notes may require us to pay immediately the principal of and accrued and unpaid interest, if any, on all of the notes.

However, at any time after the trustee or the holders, as the case may be, declare such acceleration with respect to the notes, but before the applicable person has obtained a judgment or

decree for payment of the money, the holders of a majority in principal amount of the outstanding notes may, under certain conditions, cancel such acceleration if:

•: we have deposited with the trustee an amount sufficient to pay expenses incurred by the trustee, all overdue interest, if any, on the notes and the principal of any notes that have become due and interest thereon; and
•: we have cured all events of default (other than the non-payment of accelerated principal and interest, if any) with respect to the notes or all such events of default have been waived as provided in the indenture.

The indenture provides that, subject to the duties of the trustee to act with the required standard of care if there is a continuing event of default, the trustee need not exercise any of its rights or powers under the indenture at the request or direction of any of the holders of the notes, unless such holders have offered to the trustee security or indemnity satisfactory to the trustee. Subject to such provisions for security or indemnification of the trustee and certain other conditions, the holders of the majority in principal amount of the outstanding notes will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power the trustee holds with respect to the notes.

No holder of notes will have any right to institute any proceeding with respect to the indenture or for any remedy under the indenture unless:

•: the holder has previously given the trustee written notice of a continuing event of default with respect to the notes;
•: the holders of at least 25% in principal amount of the outstanding notes have made written request to the trustee to pursue such remedy;
•: the holder or holders have offered reasonable security or indemnity to the trustee against any costs, liability or expense of the trustee;
•: the trustee has failed to comply with the request within 60 days after receipt of the request and offer of indemnity; and
•: the trustee has not received from the holders of a majority in principal amount of the outstanding notes a direction inconsistent with the request.

However, each holder of notes will have an absolute and unconditional right to receive payment of the principal of or interest on the notes on or after the date or dates it becomes due as expressed in the notes and to institute suit for the enforcement of any such payment.

We are required to furnish annually to the trustee a statement as to the existence or absence of certain defaults under the indenture. The indenture provides that the trustee need not provide to the holders of the notes notice of any default (other than the non-payment of principal or interest) if it considers it in the interest of the holders not to provide such notice.

Defeasance

Defeasance and Discharge of Indenture

We may be discharged from any and all obligations in respect of the notes (except for certain obligations to register the transfer or exchange of notes, to replace stolen, destroyed, lost or mutilated notes, to maintain paying agencies, to compensate and indemnify the trustee and to furnish the trustee with the names and addresses of holders of notes), which we refer to as defeasance, if:

•: we irrevocably deposit with the trustee, in trust, money and/or securities of the United States government, or securities of agencies of the United States government backed by the full faith

and credit of the United States government, in an amount certified by a nationally recognized firm of independent public accountants to be sufficient to pay the principal of and interest on the notes on the applicable due dates for those payments in accordance with the terms of the notes;

•: we deliver to the trustee either (i) an opinion of counsel, based on a ruling of the United States Internal Revenue Service (unless there has been a change in the applicable United States federal income tax law), to the effect that the holders of the notes will not recognize income, gain or loss for United States federal income tax purposes as a result of such defeasance and will be subject to United States federal income tax on the same amounts and in the same manner and a the same times as would have been the case if the defeasance had not occurred or (ii) a ruling of the United States Internal Revenue Service directed to the trustee to the same effect as set forth in clause (i) above;
•: immediately after giving effect to the deposit specified in the first bullet point, on a pro forma basis, no event of default with respect to the notes shall have occurred and be continuing on the date of deposit or, with respect to defaults occurring upon certain events of bankruptcy, insolvency or reorganization relating to us, at any time during the period ending on the 91st day after the date of the deposit;
•: if the notes are then listed on a national securities exchange, we deliver to the trustee an opinion of counsel to the effect that the notes will not be delisted as a result of such defeasance; and
•: we deliver to the trustee an officers' certificate and an opinion of counsel each stating that we have complied with all of the above requirements.

In addition, we may also be discharged from our obligations under the notes and the indenture (except for certain obligations specified above) if we, among other things, deposit with the trustee, in trust, money and/or government securities in an amount certified by a nationally recognized firm of independent public accountants to be sufficient to pay the principal of and interest on the notes, so long as the notes mature within one year.

Defeasance of Certain Obligations

We may omit to comply with the covenants described under "—Certain Restrictions—Limitation on Liens" and "—Consolidation and Merger" with respect to the notes, and any such omission will not constitute an event of default with respect to the notes, which we refer to as covenant defeasance, if:

•: we irrevocably deposit with the trustee, in trust, money and/or securities of the United States government, or securities of agencies of the United States government backed by the full faith and credit of the United States government, in an amount certified by a nationally recognized firm of independent public accountants to be sufficient to pay the principal of and interest on the notes on the applicable due dates for those payments in accordance with the terms of the notes;
•: we deliver to the trustee an opinion of counsel to the effect that the holders of the notes will not recognize income, gain or loss for United States federal income tax purposes as a result of such covenant defeasance and will be subject to United States federal income tax on the same amounts and in the same manner and at the same times as would have been the case if the covenant defeasance had not occurred;
•: immediately after giving effect to the deposit specified in the first bullet point, on a pro forma basis, no event of default with respect to the notes shall have occurred and be continuing on the date of the deposit or, with respect to defaults occurring upon certain events of bankruptcy,

insolvency or reorganization relating to us, at any time during the period ending on the 91st day after the date of the deposit;

•: if the notes are then listed on a national securities exchange, we deliver to the trustee an opinion of counsel to the effect that the notes will not be delisted as a result of such covenant defeasance; and
•: we deliver to the trustee an officers' certificate and an opinion of counsel each stating that we have complied with all of the above requirements.

If we exercise our option to effect a defeasance or covenant defeasance with respect to the notes, as described above, and the trustee or paying agent is unable to apply any money or securities that we have deposited because of any legal proceeding or any order or judgment of any court of governmental authority, in each case our obligations under the indenture and the notes will be revived and reinstated.

Modification of the Indenture

The indenture provides that we and the trustee may amend or supplement the indenture or the notes without notice to or the consent of any holder of the notes to, among other things:

•: cure any ambiguity, defect or inconsistency in the indenture;
•: document the fact that a successor corporation has assumed our obligations;
•: comply with any requirements of the SEC in connection with any qualification of the indenture under the Trust Indenture Act of 1939;
•: evidence and provide for the acceptance of appointment of a successor trustee;
•: provide for uncertificated notes in addition to or in place of certificated notes;
•: add to our covenants for the benefit of the holders of the notes, add any additional events of default with respect to the notes or to surrender any right or power conferred on us; or
•: make any change that, in the good faith opinion of our board of directors, does not materially and adversely affect the rights of any holder of the notes.

In addition, we and the trustee may modify the indenture or the notes with the consent of the holders of at least a majority in principal amount of the outstanding notes. However, we may not modify the indenture or the notes without the consent of each holder affected to:

•: change the due date of the principal of or any installment of interest on any note;
•: reduce the principal amount of or interest rate on any note, except as provided in the indenture;
•: change any place or currency of payment of principal of or interest on any note;
•: impair the right to institute suit for the enforcement of any payment on or after it is due (or, in the case of redemption, on or after the redemption date) on any note;
•: reduce the percentage of principal amount of outstanding notes necessary to consent to the modification or amendment of the indenture or the notes or the waiver of compliance with certain provisions of or certain defaults under the indenture;
•: waive a default in the payment of principal of or interest on any note; or
•: amend any provision relating to modification of the indenture or the notes, except to increase the percentage of principal amount of outstanding notes necessary to consent to the modification or amendment of the indenture or the notes or to provide that certain other provisions of the indenture or the notes cannot be modified or waived without the consent of each holder affected.

The holders of a majority in aggregate principal amount of the notes may, on behalf of the holders of all of the notes, waive compliance by us with any provision of the indenture or the notes, including the restrictive covenant described above under "—Certain Restrictions—Limitation on Liens." The holders of at least a majority in principal amount of the outstanding notes, by notice to the trustee, may waive any existing default and its consequences under the indenture, except for a default in the payment of the principal of or any interest on the notes or in respect of a provision which under the indenture cannot be modified or amended without the consent of each holder of the outstanding notes affected.

Consolidation and Merger

The indenture provides that we may not consolidate with or merge into, or sell, convey, transfer or lease our properties and assets substantially as an entirety to, another person without the consent of noteholders unless, along with certain other conditions in the indenture:

•: the person (if other than us) formed by such consolidation or into which we merge or which acquires or leases our assets is a corporation organized and existing under the laws of the United States, any state thereof or the District of Columbia and expressly assumes our obligations on the notes and under the indenture;
•: after giving effect to such transaction, there is no event of default, and no event which, after notice or passage of time or both, would become an event of default;
•: if, as a result of any such consolidation, merger, sale, conveyance, transfer or lease our properties or assets would become subject to a mortgage, lien or other security interest that would not be permitted under the indenture, we (or the person formed by such transaction, if other than us) take steps to secure the notes equally and ratably with all indebtedness secured thereby; and
•: we have delivered to the trustee an officers' certificate and an opinion of counsel each stating that such consolidation, merger, sale, conveyance, transfer or lease complies with these requirements.

Global Notes; Book-Entry System

Global Notes

Except as set forth below, the global original note and the global exchange note (collectively, the "global notes") may be transferred, in whole and not in part, only to DTC or another nominee of DTC or to a successor of DTC or its nominee. Beneficial interests in the global notes may not be exchanged for certificated notes except in the limited circumstances described below. The global original note, and any original notes issued in exchange therefor, will also be subject to certain restrictions on transfer set forth in this prospectus and in the offering memorandum under which the original notes were issued.

All interests in the global notes, including those held through Euroclear Bank S.A./N.V, as operator of the Euroclear System ("Euroclear"), or Clearstream Banking, société anonyme, Luxembourg ("Clearstream"), if any, may be subject to the rules and procedures of DTC. Those interests held through Euroclear or Clearstream may also be subject to the procedures and requirements of such systems.

Certain Book-Entry Procedures for the Global Notes

The descriptions of the operations and procedures of DTC, Euroclear and Clearstream set forth below are provided solely as a matter of convenience. These operations and procedures are solely within the control of the respective settlement systems and are subject to change by them from time to time.

Neither we nor the initial purchaser take any responsibility for these operations or procedures, and investors are urged to contact the relevant system or its participants directly to discuss these matters.

DTC has advised us that it is:

•: a limited-purpose trust company organized under the laws of the State of New York;
•: a "banking organization" within the meaning of the New York Banking Law;
•: a member of the Federal Reserve System;
•: a "clearing corporation" within the meaning of the New York Uniform Commercial Code, as amended; and
•: a "clearing agency" registered pursuant to Section 17A of the Exchange Act.

DTC was created to hold securities for its participants (collectively, the "participants") and to facilitate the clearance and settlement of securities transactions between participants through electronic book-entry changes to the accounts of its participants, thereby eliminating the need for physical transfer and delivery of certificates. DTC's participants include securities brokers and dealers (including the initial purchaser), banks and trust companies, clearing corporations and certain other organizations. Indirect access to DTC's system is also available to other entities such as banks, brokers, dealers and trust companies (collectively, the "indirect participants") that clear through or maintain a custodial relationship with a participant, either directly or indirectly. Investors who are not participants may beneficially own securities held by or on behalf of DTC only through participants or indirect participants.

We expect that, pursuant to procedures established by DTC:

•: upon deposit of each global note, DTC will credit, on its book-entry registration and transfer system, the accounts of participants with an interest in the global note; and
•: ownership of beneficial interests in the global notes will be shown on, and the transfer of ownership of beneficial interests in the global notes will be effected only through, records maintained by DTC (with respect to the interests of participants) and the participants and the indirect participants (with respect to the interests of persons other than participants).

The laws of some jurisdictions may require that some purchasers of securities take physical delivery of those securities in definitive form. Accordingly, the ability to transfer beneficial interests in the notes represented by a global note to those persons may be limited. In addition, because DTC can act only on behalf of its participants, who in turn act on behalf of persons who hold interests through participants, the ability of a person holding a beneficial interest in a global note to pledge or transfer that interest to persons or entities that do not participate in DTC's system, or to otherwise take actions in respect of that interest, may be affected by the lack of a physical security in respect of that interest.

So long as DTC or its nominee is the registered owner of a global note, DTC or that nominee, as the case may be, will be considered the sole legal owner or holder of the notes represented by that global note for all purposes of the notes and the indenture. Except as provided below, owners of beneficial interests in a global note will not be entitled to have the notes represented by that global note registered in their names, will not receive or be entitled to receive physical delivery of certificated notes and will not be considered the owners or holders of the notes represented by that beneficial interest under the indenture for any purpose, including with respect to the giving of any direction, instruction or approval to the trustee. Accordingly, each holder owning a beneficial interest in a global note must rely on the procedures of DTC and, if that holder is not a participant or an indirect participant, on the procedures of the participant through which that holder owns its interest, to exercise any rights of a holder of notes under the indenture or that global note. We understand that under existing industry practice, in the event that we request any action of holders of notes, or a holder that is an owner of a beneficial interest in a global note desires to take any action that DTC, as the holder

of that global note, is entitled to take, DTC would authorize the participants to take that action and the participants would authorize holders owning through those participants to take that action or would otherwise act upon the instruction of those holders. Neither we nor the trustee will have any responsibility or liability for any aspect of the records relating to or payments made on account of notes by DTC, or for maintaining, supervising or reviewing any records of DTC relating to the notes.

Payments with respect to the principal of and interest on a global note will be payable by the trustee to or at the direction of DTC or its nominee in its capacity as the registered holder of the global note under the indenture. Under the terms of the indenture, we and the trustee may treat the persons in whose names the notes, including the global notes, are registered as the owners thereof for the purpose of receiving payment thereon and for any and all other purposes whatsoever. Accordingly, neither we nor the trustee has or will have any responsibility or liability for the payment of those amounts to owners of beneficial interests in a global note. Payments by the participants and the indirect participants to the owners of beneficial interests in a global note will be governed by standing instructions and customary industry practice and will be the responsibility of the participants and indirect participants and not of DTC.

Transfers between participants in DTC will be effected in accordance with DTC's procedures and will be settled in same-day funds. Transfers between participants in Euroclear or Clearstream will be effected in the ordinary way in accordance with their respective rules and operating procedures.

Subject to compliance with the transfer restrictions applicable to the notes, cross-market transfers between the participants in DTC, on the one hand, and Euroclear or Clearstream participants, on the other hand, will be effected through DTC in accordance with DTC's rules on behalf of Euroclear or Clearstream, as the case may be, by its respective depositary; however, those cross-market transactions will require delivery of instructions to Euroclear or Clearstream, as the case may be, by the counterparty in that system in accordance with the rules and procedures and within the established deadlines (Brussels time) of that system. Euroclear or Clearstream, as the case may be, will, if the transaction meets its settlement requirements, deliver instructions to its respective depositary to take action to effect final settlement on its behalf by delivering or receiving interests in the relevant global notes in DTC, and making or receiving payment in accordance with normal procedures for same-day funds settlement applicable to DTC.

Euroclear participants and Clearstream participants may not deliver instructions directly to the depositaries for Euroclear or Clearstream.

Because of time zone differences, the securities account of a Euroclear or Clearstream participant purchasing an interest in a global note from a participant in DTC will be credited, and any such crediting will be reported to the relevant Euroclear or Clearstream participant, during the securities settlement processing day (which must be a business day for Euroclear and Clearstream) immediately following the settlement date of DTC. Cash received in Euroclear or Clearstream as a result of a sale of an interest in a global note by or through a Euroclear or Clearstream participant to a participant in DTC will be received with value on the settlement date of DTC, but will be available in the relevant Euroclear or Clearstream cash account only as of the business day for Euroclear or Clearstream following DTC's settlement date.

Although DTC, Euroclear and Clearstream have agreed to the foregoing procedures to facilitate transfers of interests in the global notes among participants in DTC, Euroclear and Clearstream, they are under no obligation to perform or to continue to perform those procedures, and those procedures may be discontinued at any time. Neither we nor the trustee will have any responsibility for the performance by DTC, Euroclear or Clearstream or their respective participants or indirect participants of their respective obligations under the rules and procedures governing their operations.

We obtained the information in this section and elsewhere in this prospectus concerning DTC, Euroclear and Clearstream and their respective book-entry systems from sources that we believe are reliable, but we take no responsibility for the accuracy of any of this information.

Certificated Notes

As described above, beneficial interests in the global notes generally may not be exchanged for certificated notes. However, the indenture provides that if:

•: the depositary for the global notes notifies us that it is unwilling or unable to continue as depositary for the global notes and we do not appoint a successor depositary within 90 days after we receive that notice of unwillingness or ineligibility; or
•: an event of default with respect to the notes has occurred and is continuing and the registrar for the notes has received a request from the depositary;

we will execute and the trustee will authenticate and deliver certificated notes in exchange for interests in the global notes. We anticipate that those certificated notes will be registered in such name or names as DTC instructs the trustee and that those instructions will be based upon directions received by DTC from its participants with respect to the ownership of beneficial interests in the global notes. Neither we nor the trustee shall be liable for any delay by DTC or any participant or indirect participant in identifying the owners of beneficial interests in the global notes and each of them may conclusively rely on, and will be protected in relying on, instructions from DTC for all purposes, including with respect to the registration and delivery, and the respective principal amounts, of the certificated notes to be issued.

Same-Day Payment

So long as DTC continues to make its settlement system available to us, all payments of principal of and interest on the global notes will be made by us in immediately available funds.

Applicable Law

The original notes and the indenture are, and the exchange notes will be, governed by and construed in accordance with the laws of the State of New York.

Concerning the Trustee

The Bank of New York is the trustee under the indenture. In the ordinary course of business, the trustee and its affiliates have provided and may in the future continue to provide investment banking, commercial banking and other financial services to us and our subsidiaries for which they have received and will receive compensation. The Bank of New York is serving as the exchange agent in the exchange offer.

EXCHANGE OFFER AND REGISTRATION RIGHTS

As a condition to the initial sale of the original notes, we entered into the registration rights agreement with the initial purchaser. In that agreement, we agreed to use our reasonable best efforts, at our cost, to file with the SEC and cause to become effective a registration statement (the "exchange registration statement") with respect to a registered offer (the "exchange offer") to exchange the original notes for the exchange notes.

The registration statement of which this prospectus is a part is the exchange registration statement described above, and the exchange offer described in this prospectus is the exchange offer referred to above. The terms of the exchange notes are substantially identical to the terms of the original notes, except that the exchange notes have been registered and the transfer restrictions, registration rights and provisions for additional interest in the event an exchange offer is not consummated within certain time periods relating to the original notes will not apply to the exchange notes.

If we determine that the exchange offer is not available or may not be consummated because it would violate applicable law or SEC staff interpretations, we may file after such determination a shelf registration statement (the "shelf registration statement") with respect to resales of the original notes. If we have determined to file and have caused the shelf registration statement to become effective, we will use our reasonable best efforts to keep the shelf registration statement effective until the expiration of the time period referred to in Rule 144(k) under the Securities Act with respect to the original notes, or such shorter period that will terminate when all original notes covered by the shelf registration statement have been sold pursuant to the shelf registration statement. We will, in the event of such an effective shelf registration statement, provide to each holder of original notes copies of the prospectus which is part of the shelf registration statement, notify such holders when the shelf registration statement becomes effective and take certain other actions as are required to permit resales of the original notes under the shelf registration statement. A holder that sells its original notes pursuant to the shelf registration statement:

•: generally will be required to be named as a selling securityholder in the related prospectus and to deliver a prospectus to the purchaser;
•: will be subject to certain of the civil liability provisions of the Securities Act in connection with such sales; and
•: will be bound by the provisions of the registration rights agreement that are applicable to such a holder (including indemnification obligations).

Because we did not fulfill our obligations under the registration rights agreement on or prior to September 9, 2002 (the date that was 270 days after the closing of the sale of the original notes), the annual interest rate on the original notes was increased by 0.5% thereafter until consummation of the exchange offer or the effectiveness of a shelf registration statement. Accordingly, holders of original notes will receive additional interest during the period from September 10, 2002 until the date on which we consummate the exchange offer or cause a shelf registration statement to become effective, at which time the annual interest rate on the original notes will be decreased by 0.5%.

CERTAIN U.S. FEDERAL INCOME TAX CONSEQUENCES

The following is a summary of certain of the United States federal income tax consequences of the beneficial ownership of the notes to an original purchaser of notes. The summary applies only to U.S. Holders (as defined below) who acquired original notes upon original issue at their issue price and hold original notes as capital assets. This summary does not apply to special situations, such as those of dealers in securities or currencies, financial institutions, life insurance companies, persons holding the original notes as part of a hedging or conversion transaction or a straddle, non-U.S. Holders or investors whose "functional currency" is not the United States dollar. This summary is based on the Internal Revenue Code of 1986, as amended to the date hereof (the "Code"), as well as U.S. Treasury Department regulations and administrative and judicial rulings. Legislative, judicial and administrative changes may occur, possibly with retroactive effect, that could alter or modify the continued validity of the statements and conclusions set forth below. This summary is intended as a general explanatory discussion of certain of the consequences of beneficially owning the notes and does not purport to furnish information in the level of detail or with the investor's specific tax circumstances that would be provided by an investor's own tax advisor. Accordingly, each prospective investor is urged to consult with its own tax advisor regarding the application of United States federal income tax laws, as well as any state, local, foreign or other tax laws, to their particular situations. As used herein, the term "U.S. Holder" means a beneficial owner of a note who or which is, for United States federal income tax purposes:

•: a citizen or resident of the United States;
•: a corporation created or organized under the laws of the United States or any state thereof (including the District of Columbia); or
•: an estate or trust treated as a United States person under section 7701(a)(30) of the Code.

Interest Income

Interest on a note will generally be taxable as ordinary income for federal income tax purposes when received or accrued by a beneficial owner in accordance with its method of tax accounting. However, any additional interest payable upon our failure to fulfill our obligations under the registration rights agreement on or prior to September 9, 2002, as described above under "Exchange Offer and Registration Rights," should be taxable as ordinary income for federal income tax purposes when the payment is made.

Exchange of Original Notes for Exchange Notes

Under current federal income tax laws, the exchange of original notes for exchange notes (as described above under "Exchange Offer and Registration Rights") will not be a taxable event to beneficial owners of notes. The exchange notes will be treated for federal income tax purposes as a continuation of the original notes. Accordingly, a beneficial owner of an original note will have the same adjusted tax basis and holding period in the exchange note as the owner had in the original note exchanged therefor.

Disposition of Notes

Except for the exchange of the original notes for the exchange notes, upon the sale, exchange or retirement of a note, a beneficial owner of a note will recognize taxable gain or loss equal to the difference between the amount realized on the sale, exchange or retirement (not including any amount realized that is attributable to accrued but unpaid interest) and such owner's adjusted tax basis in the note. To the extent attributable to accrued but unpaid interest, the amount realized will be treated as a payment of interest. A beneficial owner's adjusted tax basis in a note will generally equal the cost of

the note to such owner, reduced by any principal payments received by the owner. Gain or loss realized on the sale, exchange or retirement of a note will generally be capital gain or loss, and will be long-term capital gain or loss if at the time of sale, exchange or retirement the note has been held for more than one year. The excess of net long-term capital gains over net short-term capital losses is generally taxed at a lower rate than ordinary income for individuals. The distinction between capital gain or loss and ordinary income or loss is also relevant for purposes of, among other things, limitations on the deductibility of capital losses.

Backup Withholding

Under federal income tax law, information reporting requirements apply to interest and principal payments made to, and to the proceeds of sale before maturity by, certain non-corporate owners of notes. In addition, a backup withholding tax at a rate equal to 30% (which rate is scheduled to be reduced in increments to 28% in 2006) applies if:

•: a non-corporate owner fails to furnish the owner's Taxpayer Identification Number ("TIN") to the payor in the manner required;
•: the non-corporate owner furnishes an incorrect TIN and the payor is so notified by the Internal Revenue Service;
•: the payor is notified by the Internal Revenue Service that the non-corporate owner has failed properly to report payments of interest and dividends; or
•: in certain circumstances, the non-corporate owner fails to certify, under penalties of perjury, that the owner has not been notified by the Internal Revenue Service that it is subject to backup withholding for failure properly to report interest and dividend payments.

PLAN OF DISTRIBUTION

Based on interpretations by SEC staff set forth in no-action letters issued to third parties, including the Exxon Capital and Morgan Stanley letters and similar letters, we believe that the exchange notes to be issued pursuant to the exchange offer in exchange for original notes may be offered for resale, resold, and otherwise transferred by any holder thereof (other than any holder which is an "affiliate" of Aon within the meaning of Rule 405 under Securities Act) without compliance with the registration and prospectus delivery provisions of the Securities Act, provided that the exchange notes are acquired in the ordinary course of the holder's business and the holder has no arrangement with any person to participate in the distribution of the exchange notes. Accordingly, any holder using the exchange offer to participate in a distribution of the exchange notes will not be able to rely on these no-action letters. For this reason, broker-dealers may not participate in the exchange offer with respect to original notes acquired for their own accounts as a result of market-making or other trading activities.

LEGAL MATTERS

The validity of the notes offered by this prospectus have been passed upon for us by Richard E. Barry, our Senior Counsel and Assistant Secretary. As of October 8, 2002, Mr. Barry owned 5,117 shares of Aon Corporation common stock, held restricted stock awards of 24,600 shares and 1,980 vested and 24,020 unvested stock options. In addition, 2,682 shares of Aon Corporation common stock held by our employee stock ownership plan and savings plan were attributable to Mr. Barry.

EXPERTS

The consolidated financial statements and the related financial statement schedules (as restated) of Aon Corporation included in Aon Corporation's Annual Report (Form 10-K/A) for the year ended December 31, 2001 have been audited by Ernst & Young LLP, independent auditors, as set forth in their report thereon included therein and incorporated herein by reference. Such consolidated financial statements and schedules are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

With respect to the unaudited condensed consolidated interim financial information for the three-month periods ended March 31, 2002 and March 31, 2001, and the three and six-month periods ended June 30, 2002 and June 30, 2001, incorporated by reference in this prospectus, Ernst & Young LLP have reported that they have applied limited procedures in accordance with professional standards for a review of such information. However, their separate reports, included in Aon Corporation's Quarterly Reports on Form 10-Q/A and Form 10-Q for the quarters ended March 31, 2002 and June 30, 2002, respectively, and incorporated herein by reference, state that they did not audit and they do not express an opinion on that interim financial information. Accordingly, the degree of reliance on their reports on such information should be restricted considering the limited nature of the review procedures applied. The independent auditors are not subject to the liability provisions of Section 11 of the Securities Act for their reports on the unaudited interim financial information because those reports are not a "report" or a "part" of the registration statement prepared or certified by the auditors within the meaning of Sections 7 and 11 of the Securities Act.

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and special reports, proxy statements and other information with the SEC. You may read and copy any document we file with the SEC at the SEC's Public Reference Room at Room 1024, 450 Fifth Street, N.W., Washington, D.C. 20549. You may obtain information on the operation of the SEC's Public Reference Room by calling the SEC at 1-800-SEC-0330. Our SEC filings are also available to the public over the Internet at the SEC's Web site at http://www.sec.gov. In addition, you may inspect our SEC filings at The New York Stock Exchange, 20 Broad Street, New York, New York 10005, the Chicago Stock Exchange, 440 South LaSalle Street, Chicago, Illinois 60605 and the London Stock Exchange, Old Broad Street, London, England EC2N1HP. You may find additional information about us at our Web site at http://www.aon.com. The information on our Web site is not a part of this prospectus.

The SEC allows us to "incorporate by reference" into this prospectus the information we file with the SEC, which means that we can disclose important information to you by referring you to those documents. Any information referenced this way is considered to be part of this prospectus, and any information that we file later with the SEC will automatically update and supercede this information. We incorporate by reference the following documents that we have previously filed with the SEC and any future filings that we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 after the date of this prospectus and before the termination of this offering:

•: Annual Report on Form 10-K for the year ended December 31, 2001, as amended by the Annual Report on Form 10-K/A filed on September 27, 2002;
•: Quarterly Report on Form 10-Q for the quarter ended March 31, 2002, as amended by the Quarterly Report on Form 10-Q/A filed on September 27, 2002;
•: Quarterly Report on Form 10-Q for the quarter ended June 30, 2002;
•: Current Reports on Form 8-K filed on April 5, 2002, May 30, 2002, August 8, 2002, August 14, 2002 (relating to our press release) and October 4, 2002; and
•: Proxy Statement for the 2002 Annual Meeting of Stockholders filed on March 11, 2002.

This prospectus is part of a registration statement we have filed with the SEC relating to the securities. As permitted by SEC rules, this prospectus does not contain all of the information included in the registration statement and the accompanying exhibits we file with the SEC. You may refer to the registration statement and the exhibits for more information about us and our securities. The registration statement and exhibits are also available through the SEC's Web site.

You may receive a copy of these filings, at no cost, by writing or telephoning us at the following address and phone number:

Aon Corporation
200 East Randolph Street
Chicago, Illinois 60601
Telephone: (312) 381-1000
Attention: Corporate Secretary

Aon Corporation

Offer to Exchange
Up to $250,000,000 Aggregate Principal Amount of
Our 6.20% Notes Due 2007
For Any and All of
the $250,000,000 Aggregate Principal Amount of
Our Outstanding 6.20% Notes Due 2007

, 2002

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 20. Indemnification of Directors and Officers.

The Registrant was organized under the laws of the State of Delaware and is subject to the Delaware General Corporation Law. Delaware law provides that officers and directors may receive indemnification from their corporations for certain actual or threatened lawsuits. Delaware law sets out the standard of conduct which the officers and directors must meet in order to be indemnified, the parties who are to determine whether the standard has been met and the types of expenditures which will be indemnified. Delaware law further provides that a corporation may purchase indemnification insurance, with such insurance providing indemnification for the officers and directors whether or not the corporation would have the power to indemnify them against such liability under the provisions of Delaware law.

The Registrant has adopted an article within its Second Restated Certificate of Incorporation, as amended, that provides that it will indemnify its officers and directors to the fullest extent permitted by Delaware law.

Furthermore, the Registrant is covered by insurance which will reimburse it within the policy limits for amounts it is obligated to pay in lawsuits involving officers and directors serving in such capacities in which the damages, judgments, settlements, costs, charges or expenses incurred in connection with the defense of the action, suit or proceeding are reimbursable pursuant to the law and the Second Restated Certificate of Incorporation, as amended.

Item 21. Exhibits.

Exhibits marked with an asterisk (*) are incorporated by reference to documents previously filed by the Registrant with the SEC, as indicated. All other documents listed are filed herewith.

Exhibit Number		Description
*3	(a)	Second Restated Certificate of Incorporation of the Registrant—incorporated by reference to Exhibit 3(a) to the Registrant's Annual Report on Form 10-K for the year ended December 31, 1991.
*3	(b)	Certificate of Amendment of the Registrant's Second Restated Certificate of Incorporation—incorporated by reference to Exhibit 3 to the Registrant's Quarterly Report on Form 10-Q for the quarter ended March 31, 1994.
*3	(c)	Certificate of Amendment of the Registrant's Second Restated Certificate of Incorporation—incorporated by reference to Exhibit 3 to the Registrant's Current Report on Form 8-K filed on May 9, 2000.
*3	(d)	Amended By-laws of the Registrant—incorporated by reference to Exhibit 3.2 to the Registrant's Current Report on Form 8-K filed on October 4, 2002.
*3	(e)	Certificate of Designation for the Registrant's Series C Cumulative Preferred Stock—incorporated by reference to Exhibit 4.1 to the Registrant's Current Report on Form 8-K filed on February 9, 1994.
*4	(a)	Indenture dated as of December 13, 2001 between the Registrant and The Bank of New York, as trustee (including form of note)—incorporated by reference to Exhibit (an) to the Registrant's Annual Report on Form 10-K for the year ended December 31, 2001.
4	(b)	Registration Rights Agreement dated as of December 13, 2001 between the Registrant and Morgan Stanley & Co. Incorporated.

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5		Opinion of Richard E. Barry, Senior Counsel and Assistant Secretary of the Registrant.
*12	(a)	Statement of computation of ratios of earnings to fixed charges—incorporated by reference to Exhibit 12(a) to the Registrant's Annual Report on Form 10-K/A for the year ended December 31, 2001.
*12	(b)	Statement of computation of ratios of earnings to fixed charges—incorporated by reference to Exhibit 12(a) to the Registrant's Quarterly Report on Form 10-Q for the quarter ended June 30, 2002.
15		Letter re: unaudited interim financial information.
23	(a)	Consent of Richard E. Barry (included in Exhibit 5).
23	(b)	Consent of Ernst & Young LLP.
24		Powers of Attorney.
25		Form T-1 Statement of Eligibility under the Trust Indenture Act of 1939 of The Bank of New York.
99	.1	Letter of Transmittal (including Guidelines For Certification of Taxpayer Identification Number on Substitute Form W-9).
99	.2	Notice of Guaranteed Delivery.
99	.3	Form of Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.
99	.4	Form of Letter to Clients.

Item 22. Undertakings.

The undersigned Registrant hereby undertakes:

(a)(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this Registration Statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act of 1933;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the Registration Statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the Registration Statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20% change in the maximum aggregate offering price set forth in the "Calculation of Registration Fee" table in the effective Registration Statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the Registration Statement or any material change to such information in the Registration Statement.

(2) That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new Registration Statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

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(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(4) That, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant's annual report pursuant to Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the Registration Statement shall be deemed to be a new Registration Statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(5) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the Registrant pursuant to the foregoing provisions described in Item 20, or otherwise, the Registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

The undersigned Registrant hereby further undertakes (in accordance with the corresponding lettered undertakings in Item 22 of Form S-4):

(b) To respond to requests for information that is incorporated by reference into this prospectus pursuant to Items 4, 10(b), 11, or 13 of this Form, within one business day of receipt of such request, and to send the incorporated documents by first class mail or other equally prompt means. This includes information contained in documents filed subsequent to the effective date of the Registration Statement through the date of responding to the request.

(c) To supply by means of a post-effect amendment all information concerning a transaction, and the company being acquired involved therein, that was not the subject of and included in the Registration Statement when it became effective.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the Registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago, State of Illinois, on October 9, 2002.

		Aon CORPORATION
		By:		/s/ PATRICK G. RYAN Patrick G. Ryan Chairman and Chief Executive Officer

Pursuant to the requirements of the Securities Act, this Registration Statement has been signed by the following persons in the capacities indicated on October 9, 2002.

Name		Title

/s/ PATRICK G. RYAN Patrick G. Ryan		Chairman and Chief Executive Officer (Principal Executive Officer)
/s/ HARVEY N. MEDVIN Harvey N. Medvin		Executive Vice President and Chief Financial Officer (Principal Financial and Accounting Officer)
* Edgar D. Jannotta		Director
* Lester B. Knight		Director
* Perry J. Lewis		Director
* R. Eden Martin		Director
* Andrew J. McKenna		Director
* Robert S. Morrison		Director

* Richard C. Notebaert		Director
* Michael D. O'Halleran		President, Chief Operating Officer and Director
* John W. Rogers, Jr.		Director
* Patrick G. Ryan, Jr.		Director
* George A. Schaefer		Director
/s/ RAYMOND I. SKILLING Raymond I. Skilling		Executive Vice President, Chief Counsel and Director
* Carolyn Y. Woo		Director

*By:

/s/ RAYMOND I. SKILLING

Raymond I. Skilling
Attorney-in-Fact

EXHIBIT INDEX

Exhibit Number		Description
*3	(a)	Second Restated Certificate of Incorporation of the Registrant—incorporated by reference to Exhibit 3(a) to the Registrant's Annual Report on Form 10-K for the year ended December 31, 1991.
*3	(b)	Certificate of Amendment of the Registrant's Second Restated Certificate of Incorporation—incorporated by reference to Exhibit 3 to the Registrant's Quarterly Report on Form 10-Q for the quarter ended March 31, 1994.
*3	(c)	Certificate of Amendment of the Registrant's Second Restated Certificate of Incorporation—incorporated by reference to Exhibit 3 to the Registrant's Current Report on Form 8-K filed on May 9, 2000.
*3	(d)	Amended By-laws of the Registrant—incorporated by reference to Exhibit 3.2 to the Registrant's Current Report on Form 8-K filed on October 4, 2002.
*3	(e)	Certificate of Designation for the Registrant's Series C Cumulative Preferred Stock—incorporated by reference to Exhibit 4.1 to the Registrant's Current Report on Form 8-K filed on February 9, 1994.
*4	(a)	Indenture dated as of December 13, 2001 between the Registrant and The Bank of New York, as trustee (including form of note)—incorporated by reference to Exhibit (an) to the Registrant's Annual Report on Form 10-K for the year ended December 31, 2001.
4	(b)	Registration Rights Agreement dated as of December 13, 2001 between the Registrant and Morgan Stanley & Co. Incorporated.
5		Opinion of Richard E. Barry, Senior Counsel and Assistant Secretary of the Registrant.
*12	(a)	Statement of computation of ratios of earnings to fixed charges—incorporated by reference to Exhibit 12(a) to the Registrant's Annual Report on Form 10-K/A for the year ended December 31, 2001.
*12	(b)	Statement of computation of ratios of earnings to fixed charges—incorporated by reference to Exhibit 12(a) to the Registrant's Quarterly Report on Form 10-Q for the quarter ended June 30, 2002.
15		Letter re: unaudited interim financial information.
23	(a)	Consent of Richard E. Barry (included in Exhibit 5).
23	(b)	Consent of Ernst & Young LLP.
24		Powers of Attorney.
25		Form T-1 Statement of Eligibility under the Trust Indenture Act of 1939 of The Bank of New York.
99	.1	Letter of Transmittal (including Guidelines For Certification of Taxpayer Identification Number on Substitute Form W-9).
99	.2	Notice of Guaranteed Delivery.
99	.3	Form of Letter to Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees.
99	.4	Form of Letter to Clients.

QuickLinks

SUMMARY
RISK FACTORS
SPECIAL NOTE ON FORWARD-LOOKING STATEMENTS
USE OF PROCEEDS
RATIOS OF EARNINGS TO FIXED CHARGES
THE EXCHANGE OFFER
DESCRIPTION OF THE NOTES
EXCHANGE OFFER AND REGISTRATION RIGHTS
CERTAIN U.S. FEDERAL INCOME TAX CONSEQUENCES
PLAN OF DISTRIBUTION
LEGAL MATTERS
EXPERTS
WHERE YOU CAN FIND MORE INFORMATION
PART II INFORMATION NOT REQUIRED IN PROSPECTUS
SIGNATURES
EXHIBIT INDEX
EX-4.(B) 3 a2086409zex-4_b.txt EX 4.(B) EXHIBIT 4(b) EXECUTION COPY - -------------------------------------------------------------------------------- REGISTRATION RIGHTS AGREEMENT Dated December 13, 2001 between AON CORPORATION and MORGAN STANLEY & CO. INCORPORATED - -------------------------------------------------------------------------------- REGISTRATION RIGHTS AGREEMENT THIS REGISTRATION RIGHTS AGREEMENT (the "AGREEMENT") is made and entered into on December 13, 2001 between Aon Corporation, a Delaware corporation (the "COMPANY"), and MORGAN STANLEY & CO. INCORPORATED (the "PURCHASER"). This Agreement is made pursuant to the Purchase Agreement dated December 7, 2001 between the Company and the Purchaser (the "PURCHASE AGREEMENT"), which provides for the sale by the Company to the Purchaser of $150,000,000 aggregate principal amount of the Company's floating rate notes due 2003 and $250,000,000 aggregate principal amount of its 6.20% notes due 2007 (such notes due 2007, the "SECURITIES"). In order to induce the Purchaser to enter into the Purchase Agreement, the Company has agreed to provide to the Purchaser and its direct and indirect transferees the registration rights set forth in this Agreement. The execution of this Agreement is a condition to the closing under the Purchase Agreement. In consideration of the foregoing, the parties hereto agree as follows: 1. DEFINITIONS As used in this Agreement, the following capitalized defined terms shall have the following meanings: "1933 ACT" shall mean the Securities Act of 1933, as amended from time to time. "1934 ACT" shall mean the Securities Exchange Act of 1934, as amended from time to time. "CLOSING DATE" shall mean the Closing Date as defined in the Purchase Agreement. "COMPANY" shall have the meaning set forth in the preamble and shall also include the Company's successors. "EXCHANGE OFFER" shall mean the exchange offer by the Company of Exchange Securities for Registrable Securities pursuant to Section 2(a) hereof. "EXCHANGE OFFER REGISTRATION" shall mean a registration under the 1933 Act effected pursuant to Section 2(a) hereof. "EXCHANGE OFFER REGISTRATION STATEMENT" shall mean an exchange offer registration statement on Form S-4 (or, if applicable, on another appropriate form) under the 1933 Act and all amendments and supplements to such registration statement, in each case including the Prospectus contained therein, all exhibits thereto and all material incorporated by reference therein. "EXCHANGE SECURITIES" shall mean securities issued by the Company under the Indenture containing terms identical to the Securities (except that (i) interest thereon shall accrue from the last date on which interest was paid on the Securities or, if no such interest has been paid, from December 13, 2001 and (ii) the Exchange Securities generally will not contain restrictions on transfer) and to be offered to Holders of Securities in exchange for Securities pursuant to the Exchange Offer. "HOLDER" shall mean the Purchaser, for so long as it owns any Registrable Securities, and each of its successors, assigns and direct and indirect transferees who become registered owners of Registrable Securities under the Indenture. "INDENTURE" shall mean the Indenture relating to the Securities dated as of December 13, 2001 between the Company and The Bank of New York, as trustee, and as the same may be amended from time to time in accordance with the terms thereof. "MAJORITY HOLDERS" shall mean the Holders of a majority of the aggregate principal amount of outstanding Registrable Securities; provided that whenever the consent or approval of Holders of a specified percentage of Registrable Securities is required hereunder, Registrable Securities held by the Company or any of its affiliates (as such term is defined in Rule 405 under the 1933 Act) (other than the Purchaser or subsequent Holders of Registrable Securities if such subsequent Holders are deemed to be such affiliates solely by reason of their holding of such Registrable Securities) shall not be counted in determining whether such consent or approval was given by the Holders of such required percentage or amount. "PERSON" shall mean an individual, partnership, limited liability company, corporation, trust or unincorporated organization, or a government or agency or political subdivision thereof. "PURCHASER" shall have the meaning set forth in the preamble. "PURCHASE AGREEMENT" shall have the meaning set forth in the preamble. "PROSPECTUS" shall mean the prospectus included in a Registration Statement, including any preliminary prospectus, and any such prospectus as amended or supplemented by any prospectus supplement, including a prospectus supplement with respect to the terms of the offering of any portion of the 2 Registrable Securities covered by a Shelf Registration Statement, and by all other amendments and supplements to such prospectus, and in each case including all material incorporated by reference therein. "REGISTRABLE SECURITIES" shall mean the Securities; provided, however, that the Securities shall cease to be Registrable Securities (i) when a Registration Statement with respect to such Securities shall have been declared effective under the 1933 Act and such Securities shall have been disposed of pursuant to such Registration Statement, (ii) when such Securities have been sold to the public pursuant to Rule 144(k) (or any similar provision then in force, but not Rule 144A) under the 1933 Act or (iii) when such Securities shall have ceased to be outstanding. "REGISTRATION EXPENSES" shall mean any and all expenses incident to performance of or compliance by the Company with this Agreement, including without limitation: (i) all SEC, stock exchange or National Association of Securities Dealers, Inc. registration and filing fees, (ii) all fees and expenses incurred in connection with compliance with state securities or blue sky laws (including reasonable fees and disbursements of counsel for any underwriters or Holders in connection with blue sky qualification of any of the Exchange Securities or Registrable Securities), (iii) all expenses of any Persons in preparing or assisting in preparing, word processing, printing and distributing any Registration Statement, any Prospectus, any amendments or supplements thereto, any underwriting agreements, securities sales agreements and other documents relating to the performance of and compliance with this Agreement, (iv) all rating agency fees, (v) all fees and disbursements relating to the qualification of the Indenture under applicable securities laws, (vi) the fees and disbursements of the Trustee and its counsel, (vii) the fees and disbursements of counsel for the Company and, in the event the Company determines to file a Shelf Registration Statement, the reasonable fees and disbursements of one counsel for the Holders (which counsel shall be selected by the Majority Holders and which counsel may also be counsel for the Purchaser) and (viii) the fees and disbursements of the independent public accountants of the Company, including the expenses of any special audits or "COLD COMFORT" letters required by or incident to such performance and compliance, but excluding fees and expenses of counsel to the underwriters (other than fees and expenses set forth in clause (ii) above) or the Holders and underwriting discounts and commissions and transfer taxes, if any, relating to the sale or disposition of Registrable Securities by a Holder. "REGISTRATION STATEMENT" shall mean any registration statement of the Company that covers any of the Exchange Securities or Registrable Securities pursuant to the provisions of this Agreement and all amendments and supplements to any such Registration Statement, including post-effective amendments, in each case including the Prospectus contained therein, all exhibits thereto and all material incorporated by reference therein. 3 "SEC" shall mean the Securities and Exchange Commission. "SHELF REGISTRATION" shall mean a registration effected pursuant to Section 2(b) hereof. "SHELF REGISTRATION STATEMENT" shall mean a "SHELF" registration statement of the Company pursuant to the provisions of Section 2(b) of this Agreement which covers all of the Registrable Securities but no other securities unless approved by the Holders whose Registrable Securities are covered by such Shelf Registration Statement on an appropriate form under Rule 415 under the 1933 Act, or any similar rule that may be adopted by the SEC, and all amendments and supplements to such registration statement, including post-effective amendments, in each case including the Prospectus contained therein, all exhibits thereto and all material incorporated by reference therein. "TRUSTEE" shall mean the trustee with respect to the Securities under the Indenture. "UNDERWRITER" shall have the meaning set forth in Section 3 hereof. "UNDERWRITTEN REGISTRATION" or "UNDERWRITTEN OFFERING" shall mean a registration in which Registrable Securities are sold to an Underwriter for reoffering to the public. 2. REGISTRATION UNDER THE 1933 ACT. (a) To the extent not prohibited by any applicable law or applicable interpretation of the Staff of the SEC, the Company shall use its reasonable best efforts to cause to be filed an Exchange Offer Registration Statement covering the offer by the Company to the Holders to exchange all of the Registrable Securities for Exchange Securities and to have such Registration Statement remain effective until the closing of the Exchange Offer. The Company shall commence the Exchange Offer promptly after the Exchange Offer Registration Statement has been declared effective by the SEC and use its reasonable best efforts to have the Exchange Offer consummated not later than 60 days after such effective date. The Company shall commence the Exchange Offer by mailing the related exchange offer Prospectus and accompanying documents to each Holder stating, in addition to such other disclosures as are required by applicable law: (i) that the Exchange Offer is being made pursuant to this Agreement and that all Registrable Securities validly tendered and not withdrawn will be accepted for exchange; 4 (ii) the dates of acceptance for exchange (which shall be a period of at least 20 business days from the date such notice is mailed) (the "EXCHANGE DATES"); (iii) that any Registrable Security not tendered will remain outstanding and continue to accrue interest, but will not retain any rights under this Agreement; (iv) that Holders electing to have a Registrable Security exchanged pursuant to the Exchange Offer will be required to surrender such Registrable Security, together with the enclosed letters of transmittal, to the institution and at the address (located in the Borough of Manhattan, The City of New York) specified in the notice prior to the close of business on the last Exchange Date; and (v) that Holders will be entitled to withdraw their election, not later than the close of business on the last Exchange Date, by sending to the institution and at the address (located in the Borough of Manhattan, The City of New York) specified in the notice a telegram, telex, facsimile transmission or letter setting forth, among other things, the name of such Holder, the principal amount of Registrable Securities delivered for exchange and a statement that such Holder is withdrawing his election to have such Securities exchanged. As soon as practicable after the last Exchange Date, the Company shall: (i) accept for exchange Registrable Securities or portions thereof validly tendered and not withdrawn pursuant to the Exchange Offer; and (ii) deliver, or cause to be delivered, to the Trustee for cancellation all Registrable Securities or portions thereof so accepted for exchange by the Company and issue, and cause the Trustee to promptly authenticate and mail to each Holder, an Exchange Security equal in principal amount to the principal amount of the Registrable Securities surrendered by such Holder. The Company shall use its reasonable best efforts to complete the Exchange Offer as provided above and shall comply with the applicable requirements of the 1933 Act, the 1934 Act and other applicable laws and regulations in connection with the Exchange Offer. The Exchange Offer shall not be subject to any conditions, other than that the Exchange Offer does not violate applicable law or any applicable interpretation of the Staff of the SEC. The 5 Company shall inform the Purchaser of the names and addresses of the Holders to whom the Exchange Offer is made, and the Purchaser shall have the right, subject to applicable law, to contact such Holders and otherwise facilitate the tender of Registrable Securities in the Exchange Offer. (b) In the event that (i) the Company determines that the Exchange Offer Registration provided for in Section 2(a) above is not available or may not be consummated as soon as practicable after the last Exchange Date because it would violate applicable law or the applicable interpretations of the Staff of the SEC or (ii) the Exchange Offer has been completed and in the opinion of counsel for the Purchaser a Registration Statement must be filed and a Prospectus must be delivered by the Purchaser in connection with any offering or sale of Registrable Securities, the Company may cause to be filed after such determination or notice of such opinion of counsel is given to the Company, as the case may be, a Shelf Registration Statement providing for the sale by the Holders of all of the Registrable Securities and to have such Shelf Registration Statement declared effective by the SEC. In the event the Company files a Shelf Registration Statement solely as a result of the matters referred to in clause (ii) of the preceding sentence, the Company shall use its reasonable best efforts to file and have declared effective by the SEC both an Exchange Offer Registration Statement pursuant to Section 2(a) with respect to all Registrable Securities and a Shelf Registration Statement (which may be a combined Registration Statement with the Exchange Offer Registration Statement) with respect to offers and sales of Registrable Securities held by the Purchasers after completion of the Exchange Offer. If the Company has determined to file and use its reasonable best efforts to have the Shelf Registration Statement declared effective, the Company agrees to use its reasonable best efforts to keep the Shelf Registration Statement continuously effective until the expiration of the period referred to in Rule 144(k) with respect to the Registrable Securities or such shorter period that will terminate when all of the Registrable Securities covered by the Shelf Registration Statement have been sold pursuant to the Shelf Registration Statement. The Company further agrees to supplement or amend the Shelf Registration Statement if required by the rules, regulations or instructions applicable to the registration form used by the Company for such Shelf Registration Statement or by the 1933 Act or by any other rules and regulations thereunder for shelf registration or if reasonably requested by a Holder with respect to information relating to such Holder, and to use its reasonable best efforts to cause any such amendment to become effective and such Shelf Registration Statement to become usable as soon as thereafter practicable. The Company agrees to furnish to the Holders of Registrable Securities copies of any such supplement or amendment promptly after its being used or filed with the SEC. 6 (c) The Company shall pay all Registration Expenses in connection with the registration pursuant to Section 2(a) and Section 2(b). Each Holder shall pay all underwriting discounts and commissions and transfer taxes, if any, relating to the sale or disposition of such Holder's Registrable Securities pursuant to the Shelf Registration Statement. (d) An Exchange Offer Registration Statement pursuant to Section 2(a) hereof or a Shelf Registration Statement pursuant to Section 2(b) hereof will not be deemed to have become effective unless it has been declared effective by the SEC; provided, however, that, if, after it has been declared effective, the offering of Registrable Securities pursuant to a Shelf Registration Statement is interfered with by any stop order, injunction or other order or requirement of the SEC or any other governmental agency or court, such Registration Statement will be deemed not to have become effective during the period of such interference until the offering of Registrable Securities pursuant to such Registration Statement may legally resume. In the event the Exchange Offer is not consummated and the Shelf Registration Statement is not declared effective on or prior to September 9, 2002, the interest rate on the Securities will be increased by 0.5% per annum until (i) the Exchange Offer is consummated, (ii) the Shelf Registration Statement is declared effective by the SEC, or (iii) the Securities shall have ceased to be outstanding. (e) Without limiting the remedies available to the Purchaser and the Holders, the Company acknowledges that any failure by the Company to comply with its obligations under Section 2(a) and Section 2(b) hereof may result in material irreparable injury to the Purchaser or the Holders for which there is no adequate remedy at law, that it will not be possible to measure damages for such injuries precisely and that, in the event of any such failure, the Purchaser or any Holder may obtain such relief as may be required to specifically enforce the Company's obligations under Section 2(a) and Section 2(b) hereof. 3. REGISTRATION PROCEDURES. In connection with the obligations of the Company with respect to the Registration Statements pursuant to Section 2(a) and Section 2(b) (if the Company has determined to file a Shelf Registration Statement and use its reasonable best efforts to have such Shelf Registration Statement declared effective) hereof, the Company shall as expeditiously as possible: (a) prepare and file with the SEC a Registration Statement on the 7 appropriate form under the 1933 Act, which form (x) shall be selected by the Company and (y) shall, in the case of a Shelf Registration, be available for the sale of the Registrable Securities by the selling Holders thereof and (z) shall comply as to form in all material respects with the requirements of the applicable form and include all financial statements required by the SEC to be filed therewith, and use its reasonable best efforts to have such Registration Statement become effective and remain effective in accordance with Section 2 hereof; (b) prepare and file with the SEC such amendments and post-effective amendments to each Registration Statement as may be necessary to keep such Registration Statement effective for the applicable period and cause each Prospectus to be supplemented by any required prospectus supplement and, as so supplemented, to be filed pursuant to Rule 424 under the 1933 Act; (c) in the case of a Shelf Registration, furnish to each Holder of Registrable Securities, to counsel for the Purchaser, to counsel for the Holders and to each Underwriter of an Underwritten Offering of Registrable Securities, if any, without charge, as many copies of each Prospectus, including each preliminary Prospectus, and any amendment or supplement thereto and such other documents as such Holder or Underwriter may reasonably request, in order to facilitate the public sale or other disposition of the Registrable Securities; and the Company consents to the use of such Prospectus and any amendment or supplement thereto in accordance with applicable law by each of the selling Holders of Registrable Securities and any such Underwriters in connection with the offering and sale of the Registrable Securities covered by and in the manner described in such Prospectus or any amendment or supplement thereto in accordance with applicable law; (d) use its reasonable best efforts to register or qualify the Registrable Securities under all applicable state securities or "BLUE SKY" laws of such jurisdictions as any Holder of Registrable Securities covered by a Registration Statement shall reasonably request in writing by the time the applicable Registration Statement is declared effective by the SEC, to cooperate with such Holders in connection with any filings required to be made with the National Association of Securities Dealers, Inc. and do any and all other acts and things which may be reasonably necessary or advisable to enable such Holder to consummate the disposition in each such jurisdiction of such Registrable Securities owned by such Holder; provided, however, that the Company shall not be required to (i) qualify as a foreign corporation or as a dealer in securities in any jurisdiction where it would not otherwise be required to qualify but for this Section 3(d), (ii) file any general consent to service of process or (iii) subject itself to 8 taxation in any such jurisdiction if it is not so subject; (e) in the case of a Shelf Registration, notify each Holder of Registrable Securities, counsel for the Holders and counsel for the Purchaser promptly and, if requested by any such Holder or counsel, confirm such advice in writing (i) when a Registration Statement has become effective and when any post-effective amendment thereto has been filed and becomes effective, (ii) of any request by the SEC or any state securities authority for amendments and supplements to a Registration Statement and Prospectus or for additional information after the Registration Statement has become effective, (iii) of the issuance by the SEC or any state securities authority of any stop order suspending the effectiveness of a Registration Statement or the initiation of any proceedings for that purpose, (iv) if, between the effective date of a Registration Statement and the closing of any sale of Registrable Securities covered thereby, the representations and warranties of the Company contained in any underwriting agreement, securities sales agreement or other similar agreement, if any, relating to the offering cease to be true and correct in all material respects or if the Company receives any notification with respect to the suspension of the qualification of the Registrable Securities for sale in any jurisdiction or the initiation of any proceeding for such purpose, (v) of the happening of any event during the period a Shelf Registration Statement is effective which makes any statement made in such Registration Statement or the related Prospectus untrue in any material respect or which requires the making of any changes in such Registration Statement or Prospectus in order to make the statements therein not misleading and (vi) of any determination by the Company that a post-effective amendment to a Registration Statement would be appropriate; (f) make every reasonable effort to obtain the withdrawal of any order suspending the effectiveness of a Registration Statement at the earliest possible moment and provide immediate notice to each Holder of the withdrawal of any such order; (g) in the case of a Shelf Registration, furnish to each Holder of Registrable Securities, without charge, at least one conformed copy of each Registration Statement and any post-effective amendment thereto (without documents incorporated therein by reference or exhibits thereto, unless requested), unless such documents are available on the SEC's EDGAR Website; (h) in the case of a Shelf Registration, cooperate with the selling Holders of Registrable Securities to facilitate the timely preparation and delivery of certificates representing Registrable Securities to be sold and 9 not bearing any restrictive legends and enable such Registrable Securities to be in such denominations (consistent with the provisions of the Indenture) and registered in such names as the selling Holders may reasonably request at least one business day prior to the closing of any sale of Registrable Securities; (i) in the case of a Shelf Registration, upon the occurrence of any event contemplated by Section 3(e)(v) hereof, use its reasonable best efforts to prepare and file with the SEC a supplement or post-effective amendment to a Registration Statement or the related Prospectus or any document incorporated therein by reference or file any other required document so that, as thereafter delivered to the purchasers of the Registrable Securities, such Prospectus will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in light of the circumstances under which they were made, not misleading. The Company agrees to notify the Holders to suspend use of the Prospectus as promptly as practicable after the occurrence of such an event, and the Holders hereby agree to suspend use of the Prospectus until the Company has amended or supplemented the Prospectus to correct such misstatement or omission; (j) a reasonable time prior to the filing of any Registration Statement, any Prospectus, any amendment to a Registration Statement or amendment or supplement to a Prospectus or any document which is to be incorporated by reference into a Registration Statement or a Prospectus after the initial filing of a Registration Statement, provide the Purchaser and its counsel (and, in the case of a Shelf Registration Statement, the counsel to the Holders) a reasonable opportunity to comment on such document; (k) obtain a CUSIP number for all Exchange Securities or Registrable Securities, as the case may be, not later than the effective date of a Registration Statement; (l) cause the Indenture to be qualified under the Trust Indenture Act of 1939, as amended (the "TIA"), in connection with the registration of the Exchange Securities or Registrable Securities, as the case may be, cooperate with the Trustee and the Holders to effect such changes to the Indenture as may be required for the Indenture to be so qualified in accordance with the terms of the TIA and execute, and use its reasonable best efforts to cause the Trustee to execute, all documents as may be required to effect such changes and all other forms and documents required to be filed with the SEC to enable the Indenture to be so qualified in a timely manner; 10 (m) in the case of a Shelf Registration, make available for inspection by the Holders of the Registrable Securities, any Underwriter participating in any disposition pursuant to such Shelf Registration Statement, and attorneys and accountants designated by the Holders, at reasonable times and in a reasonable manner, all financial and other records, pertinent documents and properties of the Company, and cause the respective officers, directors and employees of the Company to supply all information reasonably requested by any such representative, Underwriter, attorney or accountant in connection with a Shelf Registration Statement; provided, however, that the foregoing inspection and gathering of information shall be coordinated, on behalf of any Underwriter, by such Underwriter and, on behalf of the other parties, by one counsel designated by and on behalf of such other parties; and provided further that such persons shall first agree in writing with the Company that any information that is reasonably and in good faith designated by the Company as confidential at the time of delivery of such information shall be kept confidential by such persons unless (i) disclosure of such information is required by court or administrative order or is necessary to respond to inquiries of regulatory authorities, (ii) disclosure of such information is required by law (including any disclosure requirements pursuant to Federal securities laws in connection with the filing of the Shelf Registration Statement or the use of any Prospectus thereunder), (iii) such information becomes generally available to the public other than as a result of disclosure, directly or indirectly, or failure to safeguard by any such person, or (iv) such information becomes available to any such person on a non-confidential basis from a source other than the Company and such source is not bound by a confidentiality agreement or other obligation not to disclose such information; (n) in the case of a Shelf Registration, use its reasonable best efforts to cause all Registrable Securities to be listed on any securities exchange or any automated quotation system on which similar securities issued by the Company are then listed if requested by the Majority Holders, to the extent such Registrable Securities satisfy applicable listing requirements; (o) use its reasonable best efforts to cause the Exchange Securities or Registrable Securities, as the case may be, to be rated by two nationally recognized statistical rating organizations (as such term is defined in Rule 436(g)(2) under the 1933 Act); (p) if reasonably requested by any Holder of Registrable Securities covered by a Registration Statement, (i) promptly incorporate in a Prospectus supplement or post-effective amendment such information with respect to such Holder as such Holder reasonably requests to be 11 included therein and (ii) make all required filings of such Prospectus supplement or such post-effective amendment as soon as the Company has received notification of the matters to be incorporated in such filing; and (q) in the case of a Shelf Registration, use its reasonable best efforts to enter into such customary agreements and take all such other actions in connection therewith (including those requested by the Holders of a majority of the Registrable Securities being sold) in order to expedite or facilitate the disposition of such Registrable Securities in an Underwritten Offering and in such connection, (i) to the extent possible, make such representations and warranties to the Holders and any Underwriters of such Registrable Securities with respect to the business of the Company and its subsidiaries, the Registration Statement, Prospectus and documents incorporated by reference or deemed incorporated by reference, if any, in each case, in form, substance and scope as are customarily made by issuers to underwriters in underwritten offerings, (ii) obtain opinions of counsel to the Company (which counsel and opinions, in form, scope and substance, shall be reasonably satisfactory to the Holders and such Underwriters and their respective counsel) addressed to each selling Holder and Underwriter of Registrable Securities, covering the matters customarily covered in opinions requested in underwritten offerings, (iii) obtain "COLD COMFORT" letters from the independent certified public accountants of the Company (and, if necessary, any other certified public accountant of any subsidiary of the Company, or of any business acquired by the Company for which financial statements and financial data are or are required to be included in the Registration Statement) addressed to each selling Holder and Underwriter of Registrable Securities, such letters to be in customary form and covering matters of the type customarily covered in "COLD COMFORT" letters in connection with underwritten offerings, and (iv) deliver such documents and certificates as may be reasonably requested by the Holders of a majority in principal amount of the Registrable Securities being sold or the Underwriters, and which are customarily delivered in underwritten offerings, to evidence the continued validity of the representations and warranties of the Company made pursuant to clause (i) above and to evidence compliance with any customary conditions contained in an underwriting agreement. In the case of a Shelf Registration Statement, the Company may require each Holder of Registrable Securities to furnish to the Company such information regarding the Holder and the proposed distribution by such Holder of such Registrable Securities as the Company may from time to time reasonably request in writing. Each Holder agrees to provide such information to the Company. In the case of a Shelf Registration Statement, each Holder agrees that, upon receipt of any notice from the Company of the happening of any event of the 12 kind described in Section 3(e)(v) hereof, such Holder will forthwith discontinue disposition of Registrable Securities pursuant to a Registration Statement until such Holder's receipt of the copies of the supplemented or amended Prospectus contemplated by Section 3(i) hereof, and, if so directed by the Company, such Holder will deliver to the Company (at its expense) all copies in its possession, other than permanent file copies then in such Holder's possession, of the Prospectus covering such Registrable Securities current at the time of receipt of such notice. If the Company shall give any such notice to suspend the disposition of Registrable Securities pursuant to a Registration Statement, the Company shall extend the period during which the Registration Statement shall be maintained effective pursuant to this Agreement by the number of days during the period from and including the date of the giving of such notice to and including the date when the Holders shall have received copies of the supplemented or amended Prospectus necessary to resume such dispositions and any such suspensions may not exceed 90 days in the aggregate during any 365 day period. The Holders of Registrable Securities covered by a Shelf Registration Statement who desire to do so may sell such Registrable Securities in an Underwritten Offering. In any such Underwritten Offering, the investment banker or investment bankers and manager or managers (the "UNDERWRITERS") that will administer the offering will be selected by the Majority Holders of the Registrable Securities included in such offering. 4. INDEMNIFICATION AND CONTRIBUTION. (a) The Company agrees to indemnify and hold harmless the Purchaser, each Holder and each Person, if any, who controls the Purchaser or any such Holder within the meaning of either Section 15 of the 1933 Act or Section 20 of the 1934 Act, from and against all losses, claims, damages and liabilities (including, without limitation, any legal or other expenses reasonably incurred in connection with defending or investigating any such action or claim) caused by any untrue statement or alleged untrue statement of a material fact contained in any Registration Statement (or any amendment thereto) pursuant to which Exchange Securities or Registrable Securities were registered under the 1933 Act, including all documents incorporated therein by reference, or caused by any omission or alleged omission to state a material fact required to be stated therein or necessary to make the statements therein not misleading, or caused by any untrue statement or alleged untrue statement of a material fact contained in any Prospectus (as amended or supplemented if the Company shall have furnished any amendments or supplements thereto), or caused by any omission or alleged omission to state a material fact necessary to make the statements therein in light of the circumstances under which they were made not misleading, except insofar as such losses, claims, damages or liabilities are caused by any such untrue statement or 13 omission or alleged untrue statement or omission based upon information relating to the Purchaser or any Holder furnished to the Company in writing by Morgan Stanley & Co. Incorporated or any selling Holder expressly for use therein, provided, however, that the foregoing indemnity with respect to any such Registration Statement or Prospectus, including any document incorporated therein by reference, shall not inure to the benefit of the Purchaser or any Holder (or to the benefit of any Person controlling such Holder) from whom the Person asserting any such losses, claims, damages or liabilities purchased the Registrable Securities if such untrue statement or omission or alleged untrue statement or alleged omission made in any such Registration Statement or Prospectus, including any document incorporated therein by reference, is eliminated or remedied in an amendment or supplement thereto and a copy of the amended or supplemented Registration Statement or Prospectus has not been furnished to such person on or prior to the written confirmation of the sale of such Registrable Securities to such Person. In connection with any Underwritten Offering permitted by Section 3, the Company will also indemnify the Underwriters, if any, selling brokers, dealers and similar securities industry professionals participating in the distribution, their officers and directors and each Person who controls such Persons (within the meaning of the 1933 Act and the 1934 Act) to the same extent as provided above with respect to the indemnification of the Holders, if requested in connection with any Registration Statement. (b) Each Holder agrees, severally and not jointly, to indemnify and hold harmless the Company, the Purchaser and the other selling Holders, and each of their respective directors, officers of the Company who sign the Registration Statement and each Person, if any, who controls the Company, the Purchaser and any other selling Holder within the meaning of either Section 15 of the 1933 Act or Section 20 of the 1934 Act to the same extent as the foregoing indemnity from the Company to the Purchaser and the Holders, but only with reference to information relating to such Holder furnished to the Company in writing by such Holder expressly for use in any Registration Statement (or any amendment thereto) or any Prospectus (or any amendment or supplement thereto). (c) In case any proceeding (including any governmental investigation) shall be instituted involving any Person in respect of which indemnity may be sought pursuant to either paragraph (a) or paragraph (b) of this Section 4, such Person (the "INDEMNIFIED PARTY") shall promptly notify the Person against whom such indemnity may be sought (the "INDEMNIFYING PARTY") in writing and the indemnifying party, upon request of the indemnified party, shall retain counsel reasonably satisfactory to the indemnified party to represent the indemnified party and any others the indemnifying party may designate in such proceeding and 14 shall pay the fees and disbursements of such counsel related to such proceeding. In any such proceeding, any indemnified party shall have the right to retain its own counsel, but the fees and expenses of such counsel shall be at the expense of such indemnified party unless (i) the indemnifying party and the indemnified party shall have mutually agreed to the retention of such counsel or (ii) the named parties to any such proceeding (including any impleaded parties) include both the indemnifying party and the indemnified party and representation of both parties by the same counsel would be inappropriate due to actual or potential differing interests between them. It is understood that the indemnifying party shall not, in connection with any proceeding or related proceedings in the same jurisdiction, be liable for (A) the fees and expenses of more than one separate firm (in addition to any local counsel) for the Purchaser and all Persons, if any, who control the Purchaser within the meaning of either Section 15 of the 1933 Act or Section 20 of the 1934 Act, (B) the fees and expenses of more than one separate firm (in addition to any local counsel) for the Company, its directors, its officers who sign the Registration Statement and each Person, if any, who controls the Company within the meaning of either such Section and (C) the fees and expenses of more than one separate firm (in addition to any local counsel) for all Holders and all Persons, if any, who control any Holders within the meaning of either such Section, and that all such fees and expenses shall be reimbursed as they are incurred. In such case involving the Purchaser and Persons who control the Purchaser, such firm shall be designated in writing by Morgan Stanley & Co. Incorporated. In such case involving the Holders and such Persons who control any Holder, such firm shall be designated in writing by the Majority Holders. In all other cases, such firm shall be designated by the Company. The indemnifying party shall not be liable for any settlement of any proceeding effected without its written consent but, if settled with such consent or if there be a final judgment for the plaintiff, the indemnifying party agrees to indemnify the indemnified party from and against any loss or liability by reason of such settlement or judgment. Notwithstanding the foregoing sentence, if at any time an indemnified party shall have requested an indemnifying party to reimburse the indemnified party for fees and expenses of counsel as contemplated by the second and third sentences of this paragraph, the indemnifying party agrees that it shall be liable for any settlement of any proceeding effected without its written consent if (i) such settlement is entered into more than 30 days after receipt by such indemnifying party of the aforesaid request and (ii) such indemnifying party shall not have reimbursed the indemnified party for such fees and expenses of counsel in accordance with such request prior to the date of such settlement. No indemnifying party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened proceeding in respect of which such indemnified party is or could have been a party and indemnity could 15 have been sought hereunder by such indemnified party, unless such settlement includes an unconditional release of such indemnified party from all liability on claims that are the subject matter of such proceeding. (d) If the indemnification provided for in paragraph (a) or paragraph (b) of this Section 4 is unavailable to an indemnified party or insufficient in respect of any losses, claims, damages or liabilities referred to therein, then each indemnifying party under such paragraph, in lieu of indemnifying such indemnified party thereunder, shall contribute to the amount paid or payable by such indemnified party as a result of such losses, claims, damages or liabilities in such proportion as is appropriate to reflect the relative fault of the indemnifying party or parties on the one hand and of the indemnified party or parties on the other hand in connection with the statements or omissions that resulted in such losses, claims, damages or liabilities, as well as any other relevant considerations. The relative fault of the Company, the Holders and the Underwriters, if any, shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or by the Holders or the Underwriters, if any, and the parties' relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission. The Holders' respective obligations to contribute pursuant to this Section 4(d) are several in proportion to the respective principal amount of Registrable Securities of such Holder that were registered pursuant to a Registration Statement. (e) The Company and each Holder agree that it would not be just or equitable if contribution pursuant to this Section 4 were determined by pro rata allocation or by any other method of allocation that does not take account of the equitable considerations referred to in paragraph (d) above. The amount paid or payable by an indemnified party as a result of the losses, claims, damages and liabilities referred to in paragraph (d) above shall be deemed to include, subject to the limitations set forth above, any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any such action or claim. Notwithstanding the provisions of this Section 4, no Holder shall be required to indemnify or contribute any amount in excess of the amount by which the total price at which Registrable Securities were sold by such Holder exceeds the amount of any damages that such Holder has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No Person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the 1933 Act) shall be entitled to contribution from any Person who was not guilty of such fraudulent misrepresentation. The remedies provided for in this Section 4 are not exclusive and shall not limit any rights or remedies 16 which may otherwise be available to any indemnified party at law or in equity. The indemnity and contribution provisions contained in this Section 4 shall remain operative and in full force and effect regardless of (i) any termination of this Agreement, (ii) any investigation made by or on behalf of the Purchaser, any Holder or any Person controlling the Purchaser or any Holder, or by or on behalf of the Company, its officers or directors or any Person controlling the Company, (iii) acceptance of any of the Exchange Securities and (iv) any sale of Registrable Securities pursuant to a Shelf Registration Statement. 5. MISCELLANEOUS. (a) No Inconsistent Agreements. The Company has not entered into, and on or after the date of this Agreement will not enter into, any agreement which breaches the rights granted to the Holders of Registrable Securities in this Agreement or the provisions hereof. The rights granted to the Holders hereunder do not breach the rights granted to the holders of the Company's other issued and outstanding securities under any such agreements. (b) Amendments and Waivers. The provisions of this Agreement, including the provisions of this sentence, may not be amended, modified or supplemented, and waivers or consents to departures from the provisions hereof may not be given unless the Company has obtained the written consent of Holders of at least a majority in aggregate principal amount of the outstanding Registrable Securities affected by such amendment, modification, supplement, waiver or consent; provided, however, that no amendment, modification, supplement, waiver or consent to any departure from the provisions of Section 4 hereof shall be effective as against any Holder of Registrable Securities unless consented to in writing by such Holder. (c) Notices. All notices and other communications provided for or permitted hereunder shall be made in writing by hand-delivery, registered first-class mail, telex, telecopier, or any courier guaranteeing overnight delivery (i) if to a Holder, at the most current address given by such Holder to the Company by means of a notice given in accordance with the provisions of this Section 5(c), which address initially is, the address of the Purchaser set forth in the Purchase Agreement; and (ii) if to the Company, initially at the Company's address set forth in the Purchase Agreement and thereafter at such other address, notice of which is given in accordance with the provisions of this Section 5(c). All such notices and communications shall be deemed to have been duly 17 given: at the time delivered by hand, if personally delivered; five business days after being deposited in the mail, postage prepaid, if mailed; when answered back, if telexed; when receipt is acknowledged, if telecopied; and on the next business day if timely delivered to an air courier guaranteeing overnight delivery. Copies of all such notices, demands, or other communications shall be concurrently delivered by the Person giving the same to the Trustee, at the address specified in the Indenture. (d) Successors and Assigns. This Agreement shall inure to the benefit of and be binding upon the successors, assigns and transferees of each of the parties, including, without limitation and without the need for an express assignment, subsequent Holders; provided that nothing herein shall be deemed to permit any assignment, transfer or other disposition of Registrable Securities in violation of the terms of the Purchase Agreement. If any transferee of any Holder shall acquire Registrable Securities, in any manner, whether by operation of law or otherwise, such Registrable Securities shall be held subject to all of the terms of this Agreement, and by taking and holding such Registrable Securities such Person shall be conclusively deemed to have agreed to be bound by and to perform all of the terms and provisions of this Agreement and such Person shall be entitled to receive the benefits hereof. The Purchaser (in its capacity as Purchaser) shall have no liability or obligation to the Company with respect to any failure by a Holder to comply with, or any breach by any Holder of, any of the obligations of such Holder under this Agreement. (e) Purchases and Sales of Securities. The Company shall not, and shall use its reasonable best efforts to cause its affiliates (as defined in Rule 405 under the 1933 Act) not to, purchase and then resell or otherwise transfer any Securities (other than to another affiliate of the Company). (f) Third Party Beneficiary. The Holders shall be third party beneficiaries to the agreements made hereunder between the Company, on the one hand, and the Purchaser, on the other hand, and shall have the right to enforce such agreements directly to the extent it deems such enforcement necessary or advisable to protect its rights or the rights of Holders hereunder. (g) Counterparts. This Agreement may be executed in any number of counterparts and by the parties hereto in separate counterparts, each of which when so executed shall be deemed to be an original and all of which taken together shall constitute one and the same agreement. (h) Headings. The headings in this Agreement are for 18 convenience of reference only and shall not limit or otherwise affect the meaning hereof. (i) Governing Law. This Agreement shall be governed by the laws of the State of New York. (j) Severability. In the event that any one or more of the provisions contained herein, or the application thereof in any circumstance, is held invalid, illegal or unenforceable, the validity, legality and enforceability of any such provision in every other respect and of the remaining provisions contained herein shall not be affected or impaired thereby. 19 IN WITNESS WHEREOF, the parties have executed this Agreement as of the date first written above. AON CORPORATION By: /s/ Patrick G. Ryan -------------------------------- Name: Patrick G. Ryan Title: Chairman and Chief Executive Officer Confirmed and accepted as of the date first above written: MORGAN STANLEY & CO. INCORPORATED By: /s/ Harold J. Hendershot III ----------------------------------------- Name: Harold J. Hendershot III Title: Executive Director 20 EX-5 4 a2086409zex-5.txt EX 5 EXHIBIT 5 OPINION OF RICHARD E. BARRY October 9, 2002 Aon Corporation 200 East Randolph Street Chicago, Illinois 60601 Re: $250,000,000 AGGREGATE PRINCIPAL AMOUNT OF 6.20% NOTES DUE 2007 Ladies and Gentlemen: I am Senior Counsel and Assistant Secretary of Aon Corporation (the "Company"). I refer to the Registration Statement on Form S-4 (the "Registration Statement") being filed by the Company with the Securities and Exchange Commission (the "SEC") under the Securities Act of 1933, as amended (the "Securities Act"), to register up to $250,000,000 aggregate principal amount of the Company's 6.20% Notes due 2007 (the "Exchange Notes") to be issued in an exchange offer for the $250,000,000 aggregate principal amount of the Company's outstanding 6.20% Notes due 2007 (the "Original Notes"). The Original Notes and the Exchange Notes are referred to herein collectively as the "Notes." Original Notes that are accepted for exchange for Exchange Notes will be cancelled and retired. The Original Notes were and the Exchange Notes will be issued pursuant to an Indenture dated as of December 13, 2001 (the "Indenture") between the Company and The Bank of New York, as trustee. The Original Notes were issued and sold on December 13, 2001 to Morgan Stanley & Co. Incorporated, the initial purchaser thereof (the "Initial Purchaser"), without registration under the Securities Act, and were offered and sold by the Initial Purchaser to qualified institutional buyers in reliance on Rule 144A under the Securities Act. In connection with the offer and sale of the Original Notes, the Company entered into a Registration Rights Agreement dated as of December 13, 2001 (the "Registration Rights Agreement") with the Initial Purchaser, providing for the registration or exchange of the Original Notes. The Registration Statement is being filed pursuant to the Registration Rights Agreement. I am familiar with the proceedings to date with respect to the proposed issuance of the Exchange Notes and have examined such records, documents and questions of law, and satisfied myself as to such matters of fact, as I have considered relevant and necessary as a basis for this opinion. In rendering the opinions expressed below, I have assumed the authenticity of all documents submitted to me as originals and the conformity to the originals of all documents submitted to me as copies. In addition, I have assumed and have not verified the accuracy as to factual matters of each document I reviewed. Based on the foregoing, I am of the opinion that: 1. The Company is duly incorporated and validly existing under the laws of the State of Delaware. 2. The Original Notes have been duly authorized and legally issued and constitute valid and binding obligations of the Company (except to the extent enforceability may be limited by applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent transfer or other similar laws Aon Corporation October 9, 2002 Page 2 affecting the enforcement of creditors' rights generally and by the effect of general principles of equity, regardless of whether enforceability is considered in a proceeding in equity or at law). 3. The Exchange Notes have been duly authorized and, when executed, authenticated and delivered pursuant to the Indenture and the Registration Rights Agreement, will be legally issued and will constitute valid and binding obligations of the Company (except to the extent enforceability may be limited by applicable bankruptcy, insolvency, moratorium, fraudulent transfer or other similar laws affecting the enforcement of creditors' rights generally and by the effect of general principles of equity, regardless of whether enforceability is considered in a proceeding in equity or at law). This opinion letter is limited to the General Corporation Law of the State of Delaware. I do not find it necessary for the purposes of this opinion letter to cover, and accordingly I express no opinion as to, the application of the securities or blue sky laws of the various states or the District of Columbia to the issuance of the Exchange Notes in exchange for the Original Notes. I hereby consent to the filing of this opinion letter as an Exhibit to the Registration Statement and to all references to me under the caption "Legal Matters" in the Prospectus forming a part of the Registration Statement. In giving such consent, I do not thereby admit that I am within the category of persons whose consent is required by Section 7 of the Securities Act or the related rules and regulations promulgated by the SEC. Very truly yours, /s/ Richard E. Barry EX-15 5 a2086409zex-15.txt EX 15 Exhibit 15 October 8, 2002 Board of Directors and Stockholders Aon Corporation We are aware of the incorporation by reference in the Registration Statement (Form S-4) and related Prospectus of Aon Corporation for the registration of $250,000,000 6.20% Notes due 2007 of our reports dated April 29, 2002 (except for Note 1, as to which the date is August 14, 2002) and August 14, 2002 relating to the unaudited condensed consolidated interim financial statements of Aon Corporation which are included in its Form 10-Q/A and Form 10-Q for the quarters ended March 31, 2002 and June 30, 2002, respectively. /s/ERNST & YOUNG LLP EX-23.(B) 6 a2086409zex-23_b.txt EX 23.(B) EXHIBIT 23(b) CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS We consent to the reference to our firm under the caption "Experts" in the Registration Statement (Form S-4) and related Prospectus of Aon Corporation for the registration of $250,000,000 of 6.20% Notes due 2007 and to the incorporation by reference therein of our report dated February 12, 2002 (except for Note 1, as to which the date is August 14, 2002), with respect to the consolidated financial statements and the related financial statement schedules (as restated) of Aon Corporation included in its Annual Report (Form 10-K/A) for the year ended December 31, 2001 filed with the Securities and Exchange Commission. /s/ ERNST & YOUNG LLP Chicago, Illinois October 8, 2002 EX-24 7 a2086409zex-24.txt EX 24 EXHIBIT 24 POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Edgar D. Jannotta ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Lester B. Knight ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Perry J. Lewis ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ R. Eden Martin ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Andrew J. McKenna ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Robert S. Morrison ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Richard C. Notebaert ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Michael D. O'Halleran ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ John W. Rogers, Jr. ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Patrick G. Ryan, Jr. ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ George A. Schaefer ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Carolyn Y. Woo ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Patrick G. Ryan ------------------------------- POWER OF ATTORNEY KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran, Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to act without the others, his true and lawful attorneys-in-fact and agents, with full and several power of substitution and resubstitution for the undersigned and in the undersigned's name, place and stead, in any and all capacities, to sign a registration statement (the "Registration Statement") under the Securities Act of 1933, as amended, for the registration of up to $250,000,000 aggregate principal amount of 6.20% Notes due 2007 and any and all amendments and supplements thereto or to the prospectus contained therein, (including pre-effective and post-effective amendments) to such Registration Statement, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, and any and all documents relating to the qualification or registration under state Blue Sky or securities laws of such securities, granting unto such attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite or necessary to be done in and about the premises, as fully to all intents and purposes as the undersigned might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or their or his substitute or substitutes, may lawfully do or cause to be done by virtue hereof. IN WITNESS WHEREOF, the undersigned has signed his/her name effective as of July 19, 2002. /s/ Harvey N. Medvin ------------------------------- EX-25 8 a2086409zex-25.txt EX 25 ================================================================================ FORM T-1 SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF ELIGIBILITY UNDER THE TRUST INDENTURE ACT OF 1939 OF A CORPORATION DESIGNATED TO ACT AS TRUSTEE CHECK IF AN APPLICATION TO DETERMINE ELIGIBILITY OF A TRUSTEE PURSUANT TO SECTION 305(b)(2) / / --------------------------- THE BANK OF NEW YORK (Exact name of trustee as specified in its charter) New York 13-5160382 (State of incorporation (I.R.S. employer if not a U.S. national bank) identification no.) One Wall Street, New York, N.Y. 10286 (Address of principal executive offices) (Zip code) --------------------------- Aon CORPORATION (Exact name of obligor as specified in its charter) Delaware 36-3051915 (State or other jurisdiction of (I.R.S. employer incorporation or organization) identification no.) 200 East Randolph Street Chicago, Illinois 60601 (Address of principal executive offices) (Zip code) --------------------------- 6.20% Notes due 2007 (Title of the indenture securities) ================================================================================ 1. GENERAL INFORMATION. FURNISH THE FOLLOWING INFORMATION AS TO THE TRUSTEE: (a) NAME AND ADDRESS OF EACH EXAMINING OR SUPERVISING AUTHORITY TO WHICH IT IS SUBJECT.

(b) WHETHER IT IS AUTHORIZED TO EXERCISE CORPORATE TRUST POWERS. Yes. 2. AFFILIATIONS WITH OBLIGOR. IF THE OBLIGOR IS AN AFFILIATE OF THE TRUSTEE, DESCRIBE EACH SUCH AFFILIATION. None. 16. LIST OF EXHIBITS. EXHIBITS IDENTIFIED IN PARENTHESES BELOW, ON FILE WITH THE COMMISSION, ARE INCORPORATED HEREIN BY REFERENCE AS AN EXHIBIT HERETO, PURSUANT TO RULE 7a-29 UNDER THE TRUST INDENTURE ACT OF 1939 (THE "ACT") AND 17 C.F.R. 229.10(d). 1. A copy of the Organization Certificate of The Bank of New York (formerly Irving Trust Company) as now in effect, which contains the authority to commence business and a grant of powers to exercise corporate trust powers. (Exhibit 1 to Amendment No. 1 to Form T-1 filed with Registration Statement No. 33-6215, Exhibits 1a and 1b to Form T-1 filed with Registration Statement No. 33-21672 and Exhibit 1 to Form T-1 filed with Registration Statement No. 33-29637.) 4. A copy of the existing By-laws of the Trustee. (Exhibit 4 to Form T-1 filed with Registration Statement No. 33-31019.) -2- 6. The consent of the Trustee required by Section 321(b) of the Act. (Exhibit 6 to Form T-1 filed with Registration Statement No. 33-44051.) 7. A copy of the latest report of condition of the Trustee published pursuant to law or to the requirements of its supervising or examining authority. -3- SIGNATURE Pursuant to the requirements of the Act, the Trustee, The Bank of New York, a corporation organized and existing under the laws of the State of New York, has duly caused this statement of eligibility to be signed on its behalf by the undersigned, thereunto duly authorized, all in The City of New York, and State of New York, on the 4th day of October, 2002. THE BANK OF NEW YORK By: /s/ MARY BETH LEWICKI ----------------------------------- Name: MARY BETH LEWICKI Title: VICE PRESIDENT -4- EXHIBIT 7 Consolidated Report of Condition of THE BANK OF NEW YORK of One Wall Street, New York, N.Y. 10286 And Foreign and Domestic Subsidiaries, a member of the Federal Reserve System, at the close of business June 30, 2002, published in accordance with a call made by the Federal Reserve Bank of this District pursuant to the provisions of the Federal Reserve Act.

Total assets........................................... $ 78,101,914 ============= LIABILITIES Deposits: In domestic offices................................. $ 29,456,619 Noninterest-bearing................................. 11,393,028 Interest-bearing.................................... 18,063,591 In foreign offices, Edge and Agreement subsidiaries, and IBFs............................ 26,667,608 Noninterest-bearing................................. 297,347 Interest-bearing.................................... 26,370,261 Federal funds purchased in domestic offices............ 1,422,522 Securities sold under agreements to repurchase......... 466,965 Trading liabilities.................................... 2,946,403 Other borrowed money: (includes mortgage indebtedness and obligations under capitalized leases)........................... 1,844,526 Bank's liability on acceptances executed and outstanding......................................... 469,319 Subordinated notes and debentures...................... 1,840,000 Other liabilities...................................... 5,998,479 ------------- Total liabilities...................................... $ 71,112,441 ============= Minority interest in consolidated subsidiaries........................................ 500,154 EQUITY CAPITAL Perpetual preferred stock and related surplus............................................. 0 Common stock........................................... 1,135,284 Surplus................................................ 1,055,509 Retained earnings...................................... 4,244,963 Accumulated other comprehensive income................. (53,563) Other equity capital components........................ 0 Total equity capital................................... 6,489,319 ------------- Total liabilities minority interest and equity capital...................................... $ 78,101,914 =============


For this type of account number	Give the SOCIAL SECURITY number of

1.	Individual	The individual
2.	Two or more individuals (joint account)	The actual owner of the account or, if combined funds, the first individual on the account (1)
3.	Custodian account of a minor (Uniform Gift to Minors Act)	The minor (2)
4.	a.	The usual revocable savings trust account (grantor is also trustee)	The grantor-trustee (1)
	b.	So-called trust account that is not a legal or valid trust under state law	The actual owner (1)

For this type of account number	Give the EMPLOYER IDENTIFICATION number of

5.	Sole proprietorship account	The owner (3)
6.	A valid trust, estate or pension trust	Legal entity (Do not furnish the identifying number of the personal representative or trustee unless the legal entity itself is not designated in the account title (4)
7.	Corporate	The corporation
8.	Association, club, religious, charitable, educational or other tax-exempt organization	The organization
9.	Partnership	The partnership
10.	A broker or registered nominee	The broker or nominee
11.	Account with the Department of Agriculture in the name of a public entity (such as a State or local government, school district or person) that receives agricultural program payments	The public entity

I, Thomas J. Mastro, Senior Vice President and Comptroller of the above-named bank do hereby declare that this Report of Condition is true and correct to the best of my knowledge and belief. Thomas J. Mastro, Senior Vice President and Comptroller We, the undersigned directors, attest to the correctness of this statement of resources and liabilities. We declare that it has been examined by us, and to the best of our knowledge and belief has been prepared in conformance with the instructions and is true and correct. Thomas A. Renyi Gerald L. Hassell Alan R. Griffith Directors EX-99.1 9 a2086409zex-99_1.htm EX 99.1
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Exhibit 99.1

Aon CORPORATION

LETTER OF TRANSMITTAL

Offer for All Outstanding
6.20% Notes Due 2007
CUSIP No. 037389 AN 3
in Exchange for
6.20% Notes Due 2007
CUSIP No. 037389 AP 8
Which Have Been Registered Under the Securities Act of 1933, as Amended

Pursuant to the Prospectus dated                        , 2002

The Registered Exchange Offer and Withdrawal Period Will Expire at 5:00 p.m.,
New York City Time, on                        , 2002, Unless Extended (the "Expiration Date")

The Exchange Agent (the "Exchange Agent") for the Exchange Offer is:

The Bank of New York

By Mail, Hand or Overnight Courier: By Facsimile:

The Bank of New York
Corporate Trust Reorganization Unit
101 Barclay 7 East
New York, New York 10286 The Bank of New York
Corporate Trust Reorganization Unit
(212) 298-1915

For Information or Confirmation by Telephone:
(212) 815-6331

        Delivery of this Letter of Transmittal to an address other than as set forth above will not constitute valid delivery.

        This Letter of Transmittal is being furnished by Aon Corporation (the "Company") in connection with its offer to exchange its 6.20% Notes due 2007 (the "Original Notes"), that were issued and sold in a transaction exempt from registration under the Securities Act of 1933, as amended (the "Securities Act"), under that certain Indenture dated as of December 13, 2001 (the "Indenture") between the Company and The Bank of New York, as trustee (the "Trustee"), for a like amount of its newly issued 6.20% Notes due 2007 (the "Exchange Notes") that have been registered under the Securities Act. The Company has prepared and delivered to holders of the Original Notes a prospectus dated                        , 2002 (the "Prospectus"). The Prospectus and this Letter of Transmittal and related materials together constitute the Company's offer (the "Exchange Offer").

        For each Original Note accepted for exchange, the holder will receive an Exchange Note having a principal amount equal to that of the surrendered Original Note. The Exchange Notes will bear interest from the most recent date to which interest has been paid on the Original Notes. Accordingly, registered holders of Exchange Notes on the relevant record date for the first interest payment date following completion of the exchange offer will receive interest accruing from the most recent date to which interest has been paid. Original notes accepted for exchange will cease to accrue interest from and after the date of completion of the exchange offer. Holders whose Original Notes are accepted for exchange will not receive any payment of interest on the Original Notes otherwise payable on any interest payment date the record date for which occurs after completion of the exchange offer.

        The exchange offer will expire at 5:00 p.m., New York City time, on                        , 2002 (the "Expiration Date') unless extended, in which case the term "Expiration Date" shall mean the last time and date to which the exchange offer is extended.

        This Letter of Transmittal is to be completed by a holder (a) if certificates representing Original Notes are to be physically delivered to the Exchange Agent herewith by the holder, (b) if tender of Original Notes is to be made by book-entry transfer to the Exchange Agent's account at The Depository Trust Company ("DTC") through the DTC Automated Tender Offer Program ("ATOP"), and an Agent's Message (as defined below) is not delivered as provided in the next paragraph, or (c) if tenders are to be made according to the guaranteed delivery procedures set forth in the prospectus under "The Exchange Offer—Guaranteed Delivery Procedures."

        Holders of Original Notes who wish to tender but whose certificates are not immediately available, or who are unable to deliver their certificates (or confirmation of the book-entry transfer of their Original Notes into the Exchange Agent's account at DTC) and all other documents required hereby to the Exchange Agent before the Expiration Date, must tender their Original Notes according to the guaranteed delivery procedures set forth in "The Exchange Offer—Guaranteed Delivery Procedures" in the prospectus. See Instructions 1 and 4. Holders of Original Notes who are tendering by book-entry transfer to the Exchange Agent's account at DTC can execute their tender through ATOP. DTC participants that are accepting the exchange offer must transmit their acceptance to DTC, which will verify the acceptance and execute a book-entry delivery to the Exchange Agent's account at DTC. DTC will then send an Agent's Message (as defined below) to the Exchange Agent for its acceptance. Delivery of the Agent's Message by DTC will satisfy the terms of the exchange offer in lieu of execution and delivery of a Letter of Transmittal by the participant(s) identified in the Agent's Message. Accordingly, this Letter of Transmittal need not be completed by a holder tendering through ATOP. As used herein, the term "Agent's Message" means, with respect to any tendered Original Notes, a message transmitted by DTC to and received by the Exchange Agent and forming part of a book-entry confirmation, stating that DTC has received an express acknowledgment from each tendering participant to the effect that, with respect to those Original Notes, the participant has received and agrees to be bound by this Letter of Transmittal and that the Company may enforce this Letter of Transmittal against the participant. Delivery of documents to DTC does not constitute delivery to the Exchange Agent.

        PLEASE READ THIS ENTIRE LETTER OF TRANSMITTAL CAREFULLY BEFORE COMPLETING ANY BOX BELOW. THE INSTRUCTIONS INCLUDED WITH THIS LETTER OF TRANSMITTAL MUST BE FOLLOWED. QUESTIONS AND REQUESTS FOR ASSISTANCE OR FOR ADDITIONAL COPIES OF THE PROSPECTUS AND LETTER OF TRANSMITTAL SHOULD BE DIRECTED TO THE EXCHANGE AGENT AT (212) 815-6331, OR AT ITS ADDRESS SET FORTH ABOVE.

        Holders who wish to tender their Original Notes must complete Box 1, Box 2 and Box 4 and must sign this Letter of Transmittal in Box 4.

2

BOX 1
TENDER OF ORIGINAL NOTES

o CHECK HERE IF CERTIFICATES REPRESENTING THE TENDERED ORIGINAL NOTES ARE ENCLOSED WITH THIS LETTER OF TRANSMITTAL.

o

CHECK HERE IF TENDERED ORIGINAL NOTES ARE BEING DELIVERED BY BOOK-ENTRY TRANSFER TO THE ACCOUNT MAINTAINED BY THE EXCHANGE AGENT WITH DTC AND COMPLETE THE FOLLOWING:

Name of Tendering Institution:



Account Number:



Transaction Code Number:



o

CHECK HERE IF TENDERED ORIGINAL NOTES ARE BEING DELIVERED PURSUANT TO A NOTICE OF GUARANTEED DELIVERY SENT TO THE EXCHANGE AGENT PRIOR TO THE DATE HEREOF AND COMPLETE THE FOLLOWING:

Name(s) of Registered Owner(s):



Date of Execution of Notice of Guaranteed Delivery:



Name of Eligible Institution which Guaranteed Delivery:



IF DELIVERED BY BOOK-ENTRY TRANSFER, COMPLETE THE FOLLOWING:

Account Number:



Transaction Code Number:



        List below the Original Notes being tendered herewith. If the space provided is inadequate, list the certificate numbers and principal amounts on a separately executed schedule and affix the schedule to this Letter of Transmittal. Tenders of Original Notes will be accepted only in principal amounts equal to $1,000 or integral multiples thereof. No alternative, conditional or contingent tenders will be accepted.

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BOX 2
DESCRIPTION OF ORIGINAL NOTES TENDERED

Name(s) and address(es) of registered holder(s),
exactly as name(s) appear(s) on Original Notes,
or on a security position
Certificate
number(s) of
Original Notes*
Aggregate
principal amount
represented by
certificate(s)
Aggregate
principal amount
tendered**















*
DOES NOT need to be completed if Original Notes are tendered by book-entry transfer.

**
Unless otherwise indicated, the holder will be deemed to have tendered the entire face amount of all Original Notes represented by tendered certificates. See Instruction 4.

        If not already printed above, the name(s) and address(es) of the registered holder(s) should be printed exactly as they appear on the certificate(s) representing the Original Notes tendered hereby or, if tendered by a participant in DTC, exactly as such participant's name appears on a security position listing as the owner of those Original Notes.

BOX 3
SPECIAL ISSUANCE/DELIVERY INSTRUCTIONS
(SEE INSTRUCTIONS 1 AND 2)

        Complete the information in the blanks below this paragraph ONLY if (1) either (a) the Exchange Notes issued in exchange for Original Notes tendered hereby, or (b) Original Notes in a principal amount not tendered or not accepted for exchange, are to be issued or reissued in the name of someone other than the person(s) whose signature(s) appear(s) within this Letter of Transmittal or sent to an address different from that shown in Box 2 entitled "Description of Original Notes Tendered" within this Letter of Transmittal, or if (2) either (a) the Exchange Notes that are delivered by book-entry transfer or (b) the Original Notes delivered by book-entry transfer which are not accepted for exchange, are to be returned by credit to an account maintained by DTC other than the account indicated in Box 1 above entitled "Tender of Original Notes."

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Issue Exchange Notes or return unexchanged Original Notes to:

Name:

Address:



(Include Zip Code)


(Tax Identification or Social Security Number)

o

Credit Exchange Notes or unexchanged Original Notes delivered by book-entry transfer to the DTC account set forth below:












        Complete the following only if certificates for Exchange Notes or for unexchanged Original Notes are to be sent to someone other that the person named above or to that person at an address other than that shown in Box 2 entitled "Description of Original Notes Tendered."

Name:

Address:



(Include Zip Code)


(Tax Identification or Social Security Number)

(See Substitute Form W-9 herein)

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NOTE: SIGNATURES MUST BE PROVIDED BELOW.
PLEASE READ THE ACCOMPANYING INSTRUCTIONS CAREFULLY.

Ladies and Gentlemen:

        The undersigned is a holder of 6.20% Notes due 2007 (the "Original Notes") issued by Aon Corporation (the "Company") under that certain Indenture dated as of December 13, 2001 (the "Indenture") between the Company and The Bank of New York, as trustee (the "Trustee").

        The undersigned acknowledges receipt of the prospectus dated                        , 2002 (the "prospectus") and this Letter of Transmittal, which together constitute the Company's offer (the "exchange offer") to exchange an aggregate principal amount of up to $250 million of its newly issued 6.20% Notes due 2007 (the "Exchange Notes") that have been registered under the Securities Act of 1933, as amended (the "Securities Act"), for a like amount of its Original Notes that were issued and sold in a transaction exempt from registration under the Securities Act.

        The undersigned hereby tenders to the Company, upon the terms and subject to the conditions set forth in the prospectus, and in accordance with this Letter of Transmittal, the principal amount of Original Notes indicated in Box 2 above labeled "Description of Original Notes Tendered" under the column heading "Principal Amount Tendered" (or, if nothing is indicated therein, with respect to the entire aggregate principal amount represented by the Original Notes described in that table). The undersigned acknowledges and agrees that Original Notes may not be tendered except in accordance with the procedures set forth in the prospectus and this Letter of Transmittal.

        Subject to, and effective upon, the acceptance for exchange of the Original Notes tendered herewith in accordance with the terms and subject to the conditions of the exchange offer, the undersigned hereby exchanges, assigns and transfers to, or upon the order of, the Company, all right, title, and interest in and to all of the Original Notes that are being tendered hereby and that are being accepted for exchange pursuant to the exchange offer. By executing this Letter of Transmittal, and subject to and effective upon acceptance for exchange of the Original Notes tendered therewith, the undersigned hereby irrevocably constitutes and appoints the Exchange Agent the true and lawful agent and attorney-in-fact of the undersigned (with full knowledge that the Exchange Agent also acts as the agent of the Company) with respect to such Original Notes, with full powers of substitution and revocation (such powers of attorney being deemed to be an irrevocable power coupled with an interest), to (i) present such Original Notes and all evidences of transfer and authenticity to, or transfer ownership of such Original Notes on the account books maintained by DTC to, or upon the order of, the Company, (ii) present such Original Notes for transfer of ownership on the books of the Company, and (iii) receive all benefits and otherwise exercise all rights of beneficial ownership of such Original Notes, all in accordance with the terms and conditions of the exchange offer.

        If the undersigned is not the registered holder of the Original Notes listed in Box 2 above labeled "Description of Original Notes Tendered" under the column heading "Principal Amount Tendered" or such registered holder's legal representative or attorney-in-fact, then in order to validly consent, the undersigned has obtained a properly completed irrevocable proxy that authorizes the undersigned (or the undersigned's legal representative or attorney-in-fact) to deliver a Letter of Transmittal in respect of such Original Notes on behalf of the registered holder thereof, and that proxy is being delivered with this Letter of Transmittal. The undersigned hereby represents and warrants that the undersigned has full power and authority to tender, exchange, assign and transfer the Original Notes tendered hereby, and that when those Original Notes are accepted for exchange by the Company, the Company will acquire good and unencumbered title thereto, free and clear of all liens, restrictions, charges and encumbrances, and those Original Notes will not be subject to any adverse claims. The undersigned will, upon request, execute and deliver any additional documents deemed by the Exchange Agent or

6

the Company to be necessary or desirable to complete the exchange, assignment and transfer of the Original Notes tendered hereby.

        The undersigned acknowledges and agrees that a tender of Original Notes pursuant to any of the procedures described in the prospectus and in this Letter of Transmittal and an acceptance of such Original Notes by the Company will constitute a binding agreement between the undersigned and the Company upon the terms and subject to the conditions of the exchange offer.

        The undersigned understands that the exchange offer will expire at 5:00 p.m., New York City time, on                        , 2002, unless extended by the Company in its sole discretion or earlier terminated (the "Expiration Date").

        No authority conferred or agreed to be conferred by this Letter of Transmittal shall be affected by, and all such authority shall survive, the death or incapacity of the undersigned, and any obligation of the undersigned hereunder shall be binding upon the heirs, executors, administrators, trustees in bankruptcy, personal and legal representatives, successors and assigns of the undersigned. This tender of Original Notes may be withdrawn at any time prior to the Expiration Date. See "The Exchange Offer—Withdrawal of Tenders" in the prospectus.

        The undersigned hereby represents and warrants that: (i) the undersigned is acquiring the Exchange Notes in the ordinary course of its business; (ii) the undersigned is not engaged in, and does not intend to engage in, a distribution of the Exchange Notes; (iii) the undersigned has no arrangement or understanding with any person to participate in the distribution of the Exchange Notes; (iv) neither the undersigned nor any other such person is an affiliate of the Company; and (v) the undersigned is not a broker-dealer who is acquiring the Exchange Notes for Original Notes acquired for its own account as a result of market-making or other trading activities.

        The undersigned also acknowledges that this exchange offer is being made in reliance upon interpretations by the staff of the SEC, as set forth in no-action letters issued to third parties, that the Exchange Notes issued in exchange for Original Notes pursuant to the exchange offer may be offered for resale, resold and otherwise transferred by holders thereof (other than any holder that is an "affiliate" of the Company within the meaning of Rule 405 under the Securities Act), without compliance with the registration and prospectus delivery provisions of the Securities Act, provided that such Exchange Notes are acquired in the ordinary course of such holders' business and the holders have no arrangement with any person to participate in the distribution of the Exchange Notes. However, the Company has not obtained a no-action letter specifically for this exchange offer, and there can be no assurance that the staff of the SEC would make a similar determination with respect to the exchange offer as in other circumstances. If any holder is an affiliate of the Company, or is engaged in or intends to engage in or has any arrangement or understanding with respect to the distribution of the Exchange Notes to be acquired pursuant to the exchange offer, that holder (a) cannot rely on the applicable interpretations of the staff of the SEC and (b) must comply with the registration and prospectus delivery requirements of the Securities Act in connection with any resale transaction.

        Original notes properly tendered and not withdrawn will be accepted as soon as practicable after the satisfaction or waiver of all conditions to the exchange offer. The undersigned understands that the Company will deliver the Exchange Notes as promptly as practicable following acceptance of the tendered Original Notes. The exchange offer is subject to a number of conditions, as more particularly set forth in the prospectus. See "The Exchange Offer—Conditions of the Exchange Offer" in the prospectus. The undersigned recognizes that as a result of these conditions the Company may not be required to accept any of the Original Notes tendered hereby. In that event, the Original Notes not accepted for exchange will be returned to the undersigned at the address shown in Box 2, "Description of Original Notes Tendered," unless otherwise indicated in Box 3, "Special Issuance/Delivery Instructions."

7

        Unless otherwise indicated in Box 3, "Special Issuance/Delivery Instructions," the undersigned hereby request(s) that any Original Notes representing principal amounts not tendered or not accepted for exchange, and that the Exchange Notes with respect to Original Notes accepted for exchange, be issued in the name(s) of, and delivered to, the undersigned (and in the case of Original Notes tendered by book-entry transfer, by credit to the account of DTC indicated therein).

        In the event that Box 3, "Special Issuance/Delivery Instructions," is completed, the undersigned hereby request(s) that any Original Notes representing principal amounts not tendered or not accepted for exchange, and that the Exchange Notes with respect to Original Notes accepted for exchange, be issued in the name(s) of, and be delivered to, the person(s) at the address(es) therein indicated, or in the case of a book-entry delivery of Original Notes, please credit the account indicated therein maintained at DTC. The undersigned recognizes that the Company has no obligation pursuant to the "Special Issuance/Delivery Instructions" box to transfer any Original Notes from the names of the registered holder(s) thereof or to issue any Exchange Notes in the name(s) of anyone other than the name(s) of the Original Notes in respect of which those Exchange Notes are issued, if the Company does not accept for exchange any of the principal amount of such Original Notes so tendered. The undersigned recognizes that the undersigned must comply with all of the terms and conditions of the Indenture as amended or supplemented from time to time in accordance with its terms to transfer Original Notes either not tendered for exchange or not accepted for exchange from the name of the registered holder(s).

        For purposes of the exchange offer, the undersigned understands that the Company will be deemed to have accepted for exchange validly tendered Original Notes (or defectively tendered Original Notes with respect to which the Company has waived the defect) if, as and when the Company gives oral (confirmed in writing) or written notice thereof to the Exchange Agent.

        The undersigned understands that the delivery and surrender of the Original Notes is not effective, and the risk of loss of the Original Notes does not pass to the Company, until receipt by the Exchange Agent of this Letter of Transmittal, or a facsimile hereof, properly completed and duly executed (or, in the case of a book-entry transfer, an Agent's Message, if applicable, in lieu of the Letter of Transmittal), together with all accompanying evidences of authority and any other required documents in a form satisfactory to the Company. All questions as to the form of all documents and the validity (including time of receipt) and acceptance of tenders and withdrawals of Original Notes will be determined by the Company in its sole discretion, which determination shall be final and binding. The undersigned has completed the appropriate boxes and signed this Letter of Transmittal to indicate the action the undersigned desires to take with respect to the exchange offer.

        The undersigned represents that it is not engaged in, and does not intend to engage in, a distribution of Exchange Notes.

8

BOX 4
PLEASE SIGN HERE
(To be completed by all tendering
holders of Original Notes regardless of whether Original Notes
are being physically delivered herewith)

        By completing, executing and delivering this Letter of Transmittal, the undersigned hereby tenders the principal amount of the Original Notes listed in Box 2 above labeled "Description of Original Notes Tendered" under the column heading "Principal Amount Tendered" (or if nothing is indicated therein, with respect to the entire aggregate principal amount represented by the Original Notes described in that box).

This Letter of Transmittal must be signed by the registered holder(s) exactly as the name(s) appear(s) on the certificate(s) representing Original Notes or, if tendered by a participant in DTC, exactly as such participant's name appears on a security position listing as the owner of those Original Notes. If signature is by trustees, executors, administrators, guardians, attorneys-in-fact, officers of corporations or others acting in a fiduciary or representative capacity, please set forth the full title and see Instruction 2.




SIGNATURE OF REGISTERED HOLDER(S) OR AUTHORIZED SIGNATORY
(SEE GUARANTEE REQUIREMENT BELOW)

Dated



Name(s)


(Please Print)

Capacity (full title)



Area Code and Telephone No.



Tax Identification or Social Security No.



MEDALLION SIGNATURE GUARANTEE
(IF REQUIRED—SEE INSTRUCTIONS 1 AND 2)

Authorized Signature:



Name of Firm:



(Place Seal Here)

COMPLETE ACCOMPANYING SUBSTITUTE FORM W-9

9

INSTRUCTIONS
FORMING PART OF THE TERMS AND CONDITIONS OF THE OFFER

        1.    Signature Guarantees.    Signatures on this Letter of Transmittal must be guaranteed by a recognized participant in the Securities Exchange Agents Medallion Program or the Stock Exchange Medallion Program (a "Medallion Signature Guarantor") (generally, a member of a registered national securities exchange or the National Association of Securities Dealers, Inc., or a commercial bank or trust company having an office in the United States (each, an "Eligible Institution")), unless (a) the Original Notes tendered hereby are tendered by a registered holder (or by a participant in DTC whose name appears on a security position listing as the owner of the Original Notes) that has not completed Box 3 entitled "Special Issuance/Delivery Instructions" in this Letter of Transmittal, or (b) the Original Notes are tendered for the account of an eligible institution. If the Original Notes are registered in the name of a person other than the signer of this Letter of Transmittal, if Original Notes not accepted for exchange or not tendered are to be returned to a person other than the registered holder or if Exchange Notes are to be issued to someone other than the signatory of this Letter of Transmittal, then the signatures on this Letter of Transmittal accompanying the tendered Original Notes must be guaranteed by a Medallion Signature Guarantor as described above. See Instruction 2.

        2.    Signatures on Letter of Transmittal, Instruments of Transfer and Endorsements.    If the registered holders of the Original Notes tendered hereby sign this Letter of Transmittal, the signatures must correspond with the name(s) as written on the face of the certificate(s) without alteration, enlargement or any change whatsoever. If this Letter of Transmittal is signed by a participant in DTC whose name is shown on a security position listing as the owner of the Original Notes tendered hereby, the signature must correspond with the name shown on the security position listing as the owner of the Original Notes.

        If any of the Original Notes tendered hereby are registered in the name of two or more holders, all registered holders must sign this Letter of Transmittal. If any of the Original Notes tendered hereby are registered in different names on several certificates, it will be necessary to complete, sign and submit as many separate Letters of Transmittal as there are different registrations of certificates.

        If this Letter of Transmittal or any Original Note or instrument of transfer is signed by a trustee, executor, administrator, guardian, attorney-in-fact, agent, officer of a corporation or other person acting in a fiduciary or representative capacity, such person should so indicate when signing, and proper evidence satisfactory to the Company of such person's authority to so act must be submitted.

        When this Letter of Transmittal is signed by the registered holders of the Original Notes tendered hereby, no endorsements of the Original Notes or separate instruments of transfer are required unless payment is to be made, or Original Notes not tendered or exchanged are to be issued to a person other than the registered holders, in which case signatures on the Original Notes or instruments of transfer must be guaranteed by a Medallion Signature Guarantor.

        This Letter of Transmittal and Original Notes should be sent only to the Exchange Agent, and not to the Company or DTC.

        If this Letter of Transmittal is signed other than by the registered holder(s) of the Original Notes tendered hereby, such Original Notes must be endorsed or accompanied by appropriate instruments of transfer, and a duly completed proxy entitling the signer to tender those Original Notes on behalf of the registered holders, in any case signed exactly as the name or names of the registered holders appear on the Original Notes and signatures on those Original Notes or instruments of transfer and proxy are required and must be guaranteed by a Medallion Signature Guarantor, unless the signature is that of an eligible institution.

        3.    Transfer Taxes.    Except as set forth in this Instruction 3, the Company will pay or cause to be paid any transfer taxes with respect to the transfer of Original Notes to it, or to its order, pursuant to the exchange offer. If Exchange Notes are to be issued or delivered to, or if Original Notes not

10

tendered or exchanged are to be registered in the name of, any persons other than the registered owners, or if tendered Original Notes are registered in the name of any persons other than the persons signing this Letter of Transmittal, the amount of transfer taxes (whether imposed on the registered holder or such other person) payable on account of the transfer to such other person will be billed to the holder unless satisfactory evidence of the payment of such taxes or exemption therefrom is submitted.

        4.    Delivery of this Letter of Transmittal and Certificates; Guaranteed Delivery Procedures.    This Letter of Transmittal is to be used if (a) certificates for Original Notes are to be physically delivered to the Exchange Agent herewith, (b) tenders are to be made according to the guaranteed delivery procedures or (c) tenders are to be made pursuant to the procedures for delivery by book-entry transfer, all as set forth in the Prospectus. For holders whose Original Notes are being delivered by book-entry transfer, delivery of an Agent's Message by DTC will satisfy the terms of the exchange offer in lieu of execution and delivery of a Letter of Transmittal by the participant(s) identified in the Agent's Message.

        To validly tender Original Notes pursuant to the exchange offer, either (a) the Exchange Agent must receive a properly completed and duly executed copy of this Letter of Transmittal (or facsimile hereof) with any required signature guarantees, together with either a properly completed and duly executed Notice of Guaranteed Delivery or certificates for the Original Notes, or an Agent's Message, as the case may be, and any other documents required by this Letter of Transmittal, or (b) a holder of Original Notes must comply with the guaranteed delivery procedures set forth below.

        Holders of Original Notes who desire to tender them pursuant to the exchange offer and whose certificates representing the Original Notes are not lost but are not immediately available, or time will not permit all required documents to reach the Exchange Agent prior to 5:00 p.m., New York City time, on the Expiration Date, or who cannot complete the procedure for book-entry transfer on a timely basis, may tender their Original Notes pursuant to the guaranteed delivery procedures set forth in the Prospectus under "The Exchange Offer—Guaranteed Delivery Procedures." Pursuant to those procedures, (a) tender must be made by a firm that is a member of a registered national securities exchange or of the National Association of Securities Dealers, Inc. or by a commercial bank or trust company having an office or correspondent in the United States and, in each instance, that is a participant in the Securities Transfer Agent Medallion Program ("STAMP") or similar program (an "eligible institution"), (b) the Exchange Agent must have received from the eligible institution, prior to 5:00 p.m., New York City time, on the Expiration Date, a properly completed and duly executed Notice of Guaranteed Delivery (by mail, hand delivery, telegram, facsimile transmission or otherwise), and (c) the certificates for all physically delivered Original Notes in proper form for transfer or an Agent's Message as the case may be, together with a properly completed and duly executed Letter of Transmittal (or facsimile hereof) and all other documents required by this Letter of Transmittal, must be received by the Exchange Agent within three New York Stock Exchange trading days after the Expiration Date, all as provided in the prospectus under the caption "The Exchange Offer—Guaranteed Delivery Procedures."

        THE METHOD OF DELIVERY OF THIS LETTER OF TRANSMITTAL, THE CERTIFICATES FOR ORIGINAL NOTES AND OTHER REQUIRED DOCUMENTS IS AT THE ELECTION AND RISK OF THE TENDERING HOLDER. EXCEPT AS OTHERWISE PROVIDED HEREIN AND IN THE PROSPECTUS, DELIVERY WILL BE DEEMED MADE ONLY WHEN ACTUALLY RECEIVED BY THE EXCHANGE AGENT. IF DELIVERY IS BY MAIL, WE RECOMMEND THAT THE HOLDER USE PROPERLY INSURED, REGISTERED MAIL WITH RETURN RECEIPT REQUESTED, AND THAT THE MAILING BE MADE SUFFICIENTLY IN ADVANCE OF THE EXPIRATION DATE TO PERMIT DELIVERY TO THE EXCHANGE AGENT PRIOR TO 5:00 P.M., NEW YORK CITY TIME, ON THE EXPIRATION DATE.

11

        All questions as to the validity, form, eligibility (including time of receipt), acceptance, withdrawal and revocation of Original Notes tendered for exchange will be determined by the Company in its sole discretion, whose determination will be final and binding. The Company reserves the right to waive any defects or irregularities in the tender or conditions of the exchange offer as to any particular Original Notes. The interpretation of the Company of the terms and conditions of the exchange offer (including these Instructions) will be final and binding. Unless waived, any defects or irregularities in connection with tenders must be cured within the time determined by the Company. No alternative, conditional or contingent tenders will be accepted. Neither the Company, the Exchange Agent or any other person will be under any duty to give notice of any defects or irregularities in any tender or will incur any liability for failure to give any notice. Tenders of Original Notes will not be deemed to have been made until irregularities have been cured or waived. Any certificates constituting Original Notes received by the Exchange Agent that are not properly tendered or as to which irregularities have not been cured or waived will be returned by the Exchange Agent to the tendering holders, unless otherwise provided in this Letter of Transmittal, as soon as practicable following the Expiration Date.

        5.    Withdrawal Rights.    Original notes tendered pursuant to the exchange offer may be withdrawn, as provided below, at any time prior to 5:00 p.m., New York City time, on the Expiration Date. For the withdrawal of a tender to be effective, a written, telegraphic or facsimile transmitted notice of withdrawal must be received by the Exchange Agent at the address or number set forth above prior to the Expiration Date. Any notice of withdrawal must (a) specify the name of the person who tendered the Original Notes, (b) identify the Original Notes to be withdrawn (including the certificate number or numbers of any physically delivered Original Notes and the principal amount of the Original Notes), and (c) be signed in the same manner required by the Letter of Transmittal by which the Original Notes were tendered (including any required signature guarantees, endorsements and/or powers). All questions as to the validity, form and eligibility (including time of receipt) of notices of withdrawal will be determined by the Company, whose determination will be final and binding on all parties. The Original Notes so withdrawn, if any, will be deemed not to have been validly tendered for exchange for purposes of the exchange offer. Any Original Notes which have been tendered for exchange but which are withdrawn will be returned to the holder without cost to the holder as soon as practicable after withdrawal. Properly withdrawn Original Notes may be retendered on or prior to 5:00 p.m., New York City time, on the Expiration Date by following the procedures for tender described in this Letter of Transmittal.

        Neither the Company, the Exchange Agent nor any other person will be under any duty to give notice of any defects or irregularities in any notice of withdrawal or will incur any liability for failure to give such a notice.

        6.    Substitute Form W-9.    Each tendering holder (or other recipient of any Exchange Notes) is required to provide the Exchange Agent with a correct taxpayer identification number ("TIN"), generally the holder's Social Security or Federal Employer Identification Number, and with certain other information, on Substitute Form W-9, which is provided under "Important Tax Information" below, and to certify that the holder (or other person) is not subject to backup withholding. Failure to provide the information on the Substitute Form W-9 may subject the tendering holder (or other person) to a $50 penalty imposed by the Internal Revenue Service and 31% federal income tax backup withholding on any payment. The box in Part 3 of the Substitute Form W-9 may be checked if the tendering holder (or other person) has not been issued a TIN and has applied for a TIN or intends to apply for a TIN in the near future. If the box in Part 3 is checked and the Exchange Agent is not provided with a TIN by the time of payment, the Exchange Agent will withhold 31% on all reportable payments, if any, until a TIN is provided to the Exchange Agent.

        7.    Requests for Assistance or Additional Copies.    Any questions or requests for assistance or additional copies of the prospectus or this Letter of Transmittal may be directed to the Exchange Agent at its telephone number set forth below.

12

IMPORTANT TAX INFORMATION

        Under federal income tax law, a holder whose tendered Original Notes are accepted for payment is required to provide the Exchange Agent with the holder's current TIN on Substitute Form W-9 below, or, alternatively, to establish another basis for an exemption from backup withholding. If the holder is an individual, the TIN is his or her Social Security number. If the Exchange Agent is not provided with the correct TIN, the holder may be subject to a $50 penalty imposed by the Internal Revenue Service. In addition, any payment made to the holder or other payee with respect to Original Notes exchanged pursuant to the exchange offer may be subject to a 31% back-up withholding tax.

        Certain holders (including, among others, all corporations and certain foreign individuals) are not subject to these backup withholding and reporting requirements. In order for a foreign individual to qualify as an exempt recipient, that holder must submit to the Exchange Agent a properly completed Internal Revenue Service Form W-8 (a "Form W-8"), signed under penalties of perjury, attesting to that individual's exempt status. A Form W-8 can be obtained from the Exchange Agent. See the enclosed "Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9" for additional instructions.

        If backup withholding applies, the Exchange Agent is required to withhold 31% of any payment made to the holder or other payee. Backup withholding is not an additional tax. Rather, the federal income tax liability of persons subject to backup withholding will be reduced by the amount of tax withheld. If withholding results in an overpayment of taxes, a refund may be obtained from the Internal Revenue Service.

Purpose of Substitute Form W-9

        To prevent backup withholding on any payment made to a holder or other payee with respect to Original Notes exchanged pursuant to the exchange offer, the holder is required to notify the Exchange Agent of the holder's current TIN (or the TIN of any other payee) by completing the form below, certifying that the TIN provided on Substitute Form W-9 is correct (or that the holder is awaiting a TIN), and that (i) the holder has not been notified by the Internal Revenue Service that the holder is subject to backup withholding as a result of failure to report all interest or dividends or (ii) the Internal Revenue Service has notified the holder that the holder is no longer subject to backup withholding.

What Number to Give the Exchange Agent

        The holder is required to give the Exchange Agent the TIN (e.g. Social Security number or Federal Employer Identification Number) of the registered owner of the Original Notes. If the Original Notes are registered in more than one name or are not registered in the name of the actual owner, consult the enclosed "Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9" for additional guidance on which number to report.

13

PAYER'S NAME: AON CORPORATION

SUBSTITUTE FORM W-9

DEPARTMENT OF THE TREASURY
INTERNAL REVENUE SERVICE

PAYER'S REQUEST FOR TAXPAYER IDENTIFICATION NUMBER ("TIN") AND CERTIFICATIONS

PART 1—PLEASE PROVIDE YOUR TIN IN THE BOX AT RIGHT AND CERTIFY BY SIGNING AND DATING BELOW

Social Security Number(s)
OR
Federal Employer Identification Number(s)

PART 2—CERTIFICATION—Under penalties of perjury, I certify that:

(1)
The number shown on this form is my correct taxpayer identification number (or I am waiting for a number to be issued for me), and

(2)
I am not subject to backup withholding because: (a) I am exempt from backup withholding, or (b) I have not been notified by the Internal Revenue Service (IRS) that I am subject to backup withholding as a result of a failure to report all interest or dividends, or (c) the IRS has notified me that I am no longer subject to backup withholding.

PART 3—AWAITING TIN—o

CERTIFICATION INSTRUCTIONS—You must cross out item (2) above if you have been notified by the IRS that you are currently subject to backup withholding because of underreporting interest or dividends on your tax return.

Name

Address

(include zip code)

Signature

Date

NOTE:

FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN A $50 PENALTY IMPOSED BY THE INTERNAL REVENUE SERVICE AND BACKUP WITHHOLDING OF 31% OF ANY PAYMENTS MADE TO YOU PURSUANT TO AN OFFER. PLEASE REVIEW THE ENCLOSED GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION NUMBER ON SUBSTITUTE FORM W-9 FOR ADDITIONAL DETAILS.

NOTE:

YOU MUST COMPLETE THE FOLLOWING CERTIFICATE IF YOU CHECKED THE BOX IN PART 3 OF THE SUBSTITUTE FORM W-9.

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CERTIFICATION OF AWAITING TAXPAYER IDENTIFICATION NUMBER

        I certify under penalties of perjury that a taxpayer identification number has not been issued to me, and either (1) I have mailed or delivered an application to receive a taxpayer identification number to the appropriate Internal Revenue Service Center or Social Security Administration office or (2) I intend to mail or deliver an application in the near future. I understand that if I do not provide a taxpayer identification number by the time of payment, 31% of all reportable payments payable to me thereafter will be withheld until I provide a taxpayer identification number to the payer and that, if I do not provide my taxpayer identification number within sixty days, such retained amounts shall be remitted to the IRS as backup withholding.

Signature
Date

In order to tender, a holder should send or deliver a properly completed and signed Letter of Transmittal, certificates for the Original Notes and any other required documents to the Exchange Agent at the address set forth below or tender pursuant to DTC's Automated Tender Offer Program. The Exchange Agent for the exchange offer is:

The Bank of New York

By Mail, Hand or Overnight Courier: By Facsimile:

The Bank of New York
Corporate Trust Reorganization Unit
101 Barclay 7 East
New York, New York 10286 The Bank of New York
Corporate Trust Reorganization Unit
(212) 298-1915

For Information or Confirmation by Telephone:
(212) 815-6331

15

GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION NUMBER
ON SUBSTITUTE FORM W-9

Guidelines for Determining the Proper Identification Number to Give the Payer.

        Social Security numbers have nine digits separated by two hyphens: i.e. 000-00-0000. Employer identification number have nine digits separated by only one hyphen: i.e. 00-0000000. The table below will help determine the number to give the payer.

For this type of account number
Give the SOCIAL SECURITY number of

1. Individual The individual

2.

Two or more individuals (joint account)

The actual owner of the account or, if combined funds, the first individual on the account (1)

3.

Custodian account of a minor (Uniform Gift to Minors Act)

The minor (2)

4.

a.

The usual revocable savings trust account (grantor is also trustee)

The grantor-trustee (1)

b.

So-called trust account that is not a legal or valid trust under state law

The actual owner (1)

For this type of account number

Give the EMPLOYER IDENTIFICATION number of

5. Sole proprietorship account The owner (3)

6.

A valid trust, estate or pension trust

Legal entity (Do not furnish the identifying number of the personal representative or trustee unless the legal entity itself is not designated in the account title (4)

7.

Corporate

The corporation

8.

Association, club, religious, charitable, educational or other tax-exempt organization

The organization

9.

Partnership

The partnership

10.

A broker or registered nominee

The broker or nominee

11.

Account with the Department of Agriculture in the name of a public entity (such as a State or local government, school district or person) that receives agricultural program payments

The public entity

(1)
List first and circle the name of the person whose number you furnish.

(2)
Circle the minor's name and furnish the minor's social security number.

(3)
You must show your individual name, but you may also enter your business or "doing business as" name. You may use either your SSN or EIN.

(4)
List first and circle the name of the legal trust, estate, or pension trust.

Note: If no name is circled when there is more than one name, the number will be considered to be that of the first name issued.

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        Section references are to the Internal Revenue Code.

        Purpose of Form.—A person who is required to file an information return with the IRS must get your correct TIN to report income paid to you, real estate transactions, mortgage interest you paid, the acquisition or abandonment of secured property, cancellation of debt, or contributions you made to an IRA. Use Form W-9 to give your correct TIN to the requester (the person requesting your TIN) and, when applicable, (1) to certify the TIN you are giving is correct (or you are waiting for a number to be issued), (2) to certify you are not subject to backup withholding, or (3) to claim exemption from backup withholding if you are an exempt payee. Giving your correct TIN and making the appropriate certifications will prevent certain payments from being subject to backup withholding.

        What is Backup Withholding?—Persons making certain payments to you must withhold and pay to the IRS 31% of such payments under certain conditions. This is called "backup withholding." Payments that could be subject to backup withholding include interest, dividends, broker and barter exchange transactions, rents, royalties, nonemployee pay, and certain payments from fishing boat operators. Real estate transactions are not subject to backup withholding.

        If you give the requester your correct TIN, make the proper certifications, and report all your taxable interest and dividends on your tax return, your payments will not be subject to backup withholding. Payments you receive will be subject to backup withholding if:

1.
You do not furnish your TIN to the requester; or

2.
The IRS tells the requester that you furnished an incorrect TIN; or

3.
The IRS tells you that you are subject to backup withholding because you did not report all your interest and dividends on your tax return (for reportable interest and dividends only); or

4.
You do not certify to the requester that you are not subject to backup withholding under 3 above (for reportable interest and dividend accounts opened after 1983 only); or

5.
You do not certify your TIN. See the Part III Instructions for exceptions.

        Certain payees and payments are exempt from backup withholding and information reporting. See the Part II Instructions and the separate Instructions for the Requester of Form W-9.

        How to Get a TIN.—If you do not have a TIN, apply for one immediately. To apply, get Form SS-5, Application for a Social Security Number Card (for individuals), from your local office of the Social Security Administration, or Form SS-4, Application for Employer Identification Number (for businesses and all other entities), from your local IRS office.

        If you do not have a TIN, write "Applied For" in the space for the TIN in Part I, sign and date the form, and give it to the requester. Generally, you will then have 60 days to get a TIN and give it to the requester. If the requester does not receive your TIN within 60 days, backup withholding, if applicable, will begin and continue until you furnish your TIN.

Note: Writing "Applied For" on the form means that you have already applied for a TIN OR that you intend to apply for one soon.

        As soon as you receive your TIN, complete another Form W-9, include your TIN, sign and date the form, and give it to the requester.

Penalties

        Failure To Furnish TIN.—If you fail to furnish your correct TIN to a requester, you are subject to a penalty of $50 for each such failure unless your failure is due to reasonable cause and not to willful neglect.

17

        Civil Penalty for False Information With Respect to Withholding.—If you make a false statement with no reasonable basis that results in no backup withholding, you are subject to a $500 penalty.

        Criminal Penalty for Falsifying Information.—Willfully falsifying certifications or affirmations may subject you to criminal penalties including fines and/or imprisonment.

        Misuse of TINs.—If the requester discloses or uses TINs in violation of Federal law, the requester may be subject to civil and criminal penalties.

Specific Instructions

        Name.—If you are an individual, you must generally enter the name shown on your social security card. However, if you have changed your last name, for instance, due to marriage, without informing the Social Security Administration of the name change, please enter your name, the last name shown on your social security card and your new last name.

        Sole Proprietor.—You must enter your individual name. (Enter either your SSN or EIN in Part I). You may also enter your business name or "doing business as" name on the business name line. Enter your name as shown on your social security card and business name as it was used to apply for your EIN on Form SS-4.

Part I—Taxpayer Identification Number (TIN)

        You must enter your TIN in the appropriate box. If you are a sole proprietor, you may enter your SSN or EIN. Also see the chart on page 16 for further clarification of name and TIN combinations. If you do not have a TIN, follow the instructions under How To Get A TIN on page 17.

Part II—For Payees Exempt From Backup Withholding

        Individuals (including sole proprietors) are not exempt from backup withholding. Corporations are exempt from backup withholding for certain payments, such as interest and dividends.

        If you are exempt from backup withholding, you should still complete this form to avoid possible erroneous backup withholding. Enter your correct TIN in Part I, write "Exempt" in Part II, and sign and date the form. If you are a nonresident alien or a foreign entity not subject to backup withholding, give the requester a completed Form W-8, Certificate of Foreign Status.

Part III—Certification

        For a joint account, only the person whose TIN is shown in Part I should sign.

        1.    Interest, Dividend, and Barter Exchange Accounts Opened Before 1984 and Broker Accounts Considered Active During 1983. You must give your correct TIN, but you do not have to sign the certification.

        2.    Interest, Dividend, Broker, and Barter Exchange Accounts Opened After 1983 and Broker Accounts Considered Inactive During 1983. You must sign the certification or backup withholding will apply. If you are subject to backup withholding and you are merely providing your correct TIN to the requester, you must cross out Item 2 in the certification before signing the form.

        3.    Real Estate Transactions. You must sign the certification. You may cross out Item 2 of the certification.

        4.    Other Payments. You must give your correct TIN, but you do not have to sign the certification unless you have been notified of an incorrect TIN. Other payments include payments made in the course of the requester's trade or business for rents, royalties, goods (other than bills for merchandise),

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medical and health care services, payments to a nonemployee for services (including attorney and accounting fees), and payments to certain fishing boat crew members.

        5.    Mortgage Interest Paid by You, Acquisitions or Abandonment of Secured Property, Cancellation of Debt, or IRA Contributions. You must give your correct TIN, but you do not have to sign the certification.

Privacy Act Notice

        Section 6109 requires you to give your correct TIN to persons who must file information returns with the IRS to report interest, dividends, and certain other income paid to you, mortgage interest you paid, the acquisition or abandonment of secured property, cancellation of debt, or contributions you made to an IRA. The IRS uses the numbers for identification purposes and to help verify the accuracy of your tax return. You must provide your TIN whether or not you are required to file a tax return. Payers must generally withhold 31% of taxable interest, dividend, and certain other payments to a payee who does not give a TIN to a payer. Certain penalties may also apply.

19

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Exhibit 99.1

EX-99.2 10 a2086409zex-99_2.htm EX 99.2
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Exhibit 99.2

NOTICE OF GUARANTEED DELIVERY
for Tender of
6.20% Notes due 2007
of Aon Corporation
for Exchange

        As set forth in the Exchange Offer (as defined below), this Notice of Guaranteed Delivery (or a facsimile hereof) or one substantially equivalent hereto or the electronic form used by The Depository Trust Company ("DTC") for this purpose must be used to accept the Exchange Offer if certificates for 6.20% Notes due 2007 (the "Original Notes") of Aon Corporation, a Delaware corporation (the "Company"), are not immediately available to the registered holder of such Original Notes, or if a participant in DTC is unable to complete the procedures for book-entry transfer on a timely basis of Original Notes to the account maintained by The Bank of New York (the "Exchange Agent") at DTC, or if time will not permit all documents required by the Exchange Offer to reach the Exchange Agent prior to 5:00 p.m., New York City time, on                        , 2002, unless extended (the "Expiration Date"). This Notice of Guaranteed Delivery (or a facsimile hereof) or one substantially equivalent hereto may be delivered by mail (registered or certified mail is recommended), by facsimile transmission, by hand or overnight carrier to the Exchange Agent. See "The Exchange Offer—Procedures for Tendering Original Notes." Capitalized terms used herein and not defined herein have the meanings assigned to them in the Exchange Offer.

The Exchange Agent (the "Exchange Agent") for the Exchange Offer is:

The Bank of New York

By Mail, Hand or Overnight Courier: By Facsimile:

The Bank of New York
Corporate Trust Reorganization Unit
101 Barclay 7 East
New York, New York 10286 The Bank of New York
Corporate Trust Reorganization Unit
(212) 298-1915

For Information or Confirmation by Telephone:
(212) 815-6331

        Delivery of this Notice of Guaranteed Delivery to an address other than as set forth above or transmission of this Notice of Guaranteed Delivery via a facsimile number other than the number listed above will not constitute a valid delivery.

        This Notice of Guaranteed Delivery is not to be used to guarantee signatures. If a signature on a Letter of Transmittal is required to be guaranteed by an Eligible Institution (as defined therein) under the instructions thereto, such signature guarantee must appear in the applicable space provided in the signature box on the Letter of Transmittal.

Ladies and Gentlemen:

        The undersigned hereby tenders to Aon Corporation, a Delaware corporation (the "Company"), the aggregate principal amount of Original Notes indicated below pursuant to the guaranteed delivery procedures and upon the terms and subject to the conditions set forth in the accompanying Prospectus dated                        , 2002 (as the same may be amended or supplemented from time to time, the "Prospectus") and in the related Letter of Transmittal (which together with the Prospectus constitute the "Exchange Offer"), receipt of which is hereby acknowledged.

        The undersigned hereby represents, warrants and agrees that the undersigned has full power and authority to tender, exchange, sell, assign, and transfer the tendered Original Notes and that the Company will acquire good, marketable and unencumbered title thereto, free and clear of all liens, restrictions, charges and encumbrances when the tendered Original Notes are acquired by the Company as contemplated herein, and the tendered Original Notes are not subject to any adverse claims or proxies. The undersigned warrants and agrees that the undersigned and each Beneficial Owner will, upon request, execute and deliver any additional documents deemed by the Company or the Exchange Agent to be necessary or desirable to complete the tender, exchange, sale, assignment and transfer of the tendered Original Notes, and that the undersigned will comply with its obligations under the Registration Rights Agreement. The undersigned has read and agrees to all of the terms of the Exchange Offer.

        BY TENDERING ORIGINAL NOTES AND EXECUTING THIS NOTICE OF GUARANTEED DELIVERY, THE UNDERSIGNED HEREBY REPRESENTS AND WARRANTS THAT (i) NEITHER THE UNDERSIGNED NOR ANY BENEFICIAL OWNER(S) IS AN "AFFILIATE" OF THE COMPANY, (ii) ANY EXCHANGE NOTES TO BE RECEIVED BY THE UNDERSIGNED AND ANY BENEFICIAL OWNER(S) ARE BEING ACQUIRED BY THE UNDERSIGNED AND ANY BENEFICIAL OWNER(S) IN THE ORDINARY COURSE OF BUSINESS OF THE UNDERSIGNED AND ANY BENEFICIAL OWNER(S), (iii) THE UNDERSIGNED AND EACH BENEFICIAL OWNER HAVE NO ARRANGEMENT OR UNDERSTANDING WITH ANY PERSON TO PARTICIPATE IN A DISTRIBUTION (WITHIN THE MEANING OF THE SECURITIES ACT) OF EXCHANGE NOTES TO BE RECEIVED IN THE EXCHANGE OFFER, (iv) THE UNDERSIGNED OR ANY SUCH BENEFICIAL OWNER IS NOT ENGAGED IN, AND DOES NOT INTEND TO ENGAGE IN, A DISTRIBUTION (WITHIN THE MEANING OF THE SECURITIES ACT) OF SUCH EXCHANGE NOTES, AND (v) THE UNDERSIGNED IS NOT A BROKER-DEALER WHO IS ACQUIRING EXCHANGE NOTES FOR ORIGINAL NOTES ACQUIRED FOR ITS OWN ACCOUNT AS A RESULT OF MARKET-MAKING OR OTHER TRADING ACTIVITIES.

        All questions as to the form of documents, validity, eligibility (including time of receipt) and acceptance for exchange of tendered Original Notes will be determined by the Company, in its sole discretion, whose determination shall be final and binding on all parties. The Company reserves the absolute right, in its sole and absolute discretion, to reject any and all tenders determined by the Company not to be in proper form or the acceptance of which, or exchange for, may, in the view of the Company or its counsel, be unlawful.

        All authority herein conferred or agreed to be conferred shall survive the death or incapacity of the undersigned and every obligation of the undersigned hereunder shall be binding upon the heirs,

2

executors, administrators, personal representatives, trustees in bankruptcy, legal representatives, successors and assigns of the undersigned.

Name(s) of Registered Holder(s):




Please Print

Address(es):





Area Code and Tel. No(s):



x


x

Signature(s) of Owner(s) or Authorized Signatory

        Must be signed by the registered holder(s) of the tendered Original Notes as their name(s) appear(s) on certificates for such tendered Original Notes, or on a security position listing, or by person(s) authorized to become registered holder(s) by endorsement and documents transmitted with this Notice of Guaranteed Delivery. If signature is by a trustee, executor, administrator, guardian, attorney-in-fact, officer or other person acting in a fiduciary or representative capacity, such person must set forth his or her full title below.

Certificate No(s)
(if available)
Aggregate Principal
Amount Represented
by Certificate
Aggregate Principal
Amount Tendered











        If Original Notes will be delivered by book-entry transfer to The Depository Trust Company, provide the following information:

Signature:

Account Number:



Date:



THE GUARANTEE ON THE REVERSE SIDE MUST BE COMPLETED

3

GUARANTEE
(Not to be used for signature guarantee)

        The undersigned, a firm or other entity identified in Rule 17Ad-15 under the Securities Exchange Act of 1934, as amended, as an "eligible guarantor institution," including (as such terms are defined therein): (i) a bank; (ii) a broker, dealer, municipal securities broker, municipal securities dealer, government securities broker, government securities dealer; (iii) a credit union; (iv) a national securities exchange, registered securities association or clearing agency; or (v) a savings association that is a participant in a Securities Transfer Association recognized program (each of the foregoing being referred to as an "Eligible Institution"), hereby guarantees delivery to the Exchange Agent, at one of its addresses set forth above, either certificates for the Original Notes tendered hereby, in proper form for transfer, or confirmation of the book-entry transfer of such Original Notes to the Exchange Agent's account at The Depository Trust Company ("DTC"), pursuant to the procedures for book-entry transfer set forth in the Prospectus, in either case together with one or more properly completed and duly executed Letter(s) of Transmittal (or facsimile thereof or an Agent's Message in lieu thereof) and any other documents required by the Letter of Transmittal, all within five (5) business days after the date of execution of this Notice of Guaranteed Delivery.

        The undersigned acknowledges that it must communicate the guarantee to the Exchange Agent and must deliver the Letter of Transmittal and certificates for the Original Notes tendered hereby to the Exchange Agent within the time period shown hereon and that failure to do so could result in a financial loss to the undersigned.



Firm


Authorized Signature


Address

Name


(Please Type or Print)


Zip Code

Title



Dated



, 2002

Area Code and Tel. No.:



        DO NOT SEND CERTIFICATES FOR ORIGINAL NOTES WITH THIS NOTICE OF GUARANTEED DELIVERY. ACTUAL SURRENDER OF ORIGINAL NOTES MUST BE MADE PURSUANT TO, AND BE ACCOMPANIED BY, A PROPERLY COMPLETED AND DULY EXECUTED LETTER OF TRANSMITTAL AND ANY OTHER REQUIRED DOCUMENTS.

4

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Exhibit 99.2

EX-99.3 11 a2086409zex-99_3.htm EX 99.3
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Exhibit 99.3

AON CORPORATION

OFFER TO EXCHANGE
Its
6.20% Notes due 2007
Which Have Been Registered Under the Securities Act of 1933
for Any and All of Its Outstanding
6.20% Notes due 2007

                        , 2002

To Brokers, Dealers, Commercial Banks,
Trust Companies and Other Nominees:

        We are enclosing herewith an offer by Aon Corporation, a Delaware corporation (the "Company"), to exchange the Company's new 6.20% Notes due 2007 (the "Exchange Notes") which have been registered under the Securities Act of 1933, as amended (the "Securities Act"), for any and all of the Company's outstanding 6.20% Notes due 2007 (the "Original Notes"), upon the terms and subject to the conditions set forth in the accompanying Prospectus, dated                        , 2002 (as the same amended and supplemented from time to time, the "Prospectus"), and related Letter of Transmittal (which together with the Prospectus constitutes the "Exchange Offer").

        The Exchange Offer provides a procedure for holders to tender the Original Notes by means of guaranteed delivery.

        The Exchange Offer will expire at 5:00 p.m., New York City time, on                        , 2002, unless extended (the "Expiration Date"). Tendered Original Notes may be withdrawn at any time prior to 5:00 p.m., New York City time, on the Expiration Date, if such Original Notes have not previously been accepted for exchange pursuant to the Exchange Offer.

        Based on an interpretation by the staff of the Division of Corporation Finance of the Securities and Exchange Commission (the "SEC") as set forth in certain interpretive letters addressed to third parties in other transactions, Exchange Notes issued pursuant to the Exchange Offer in exchange for Original Notes may be offered for resale, resold and otherwise transferred by a holder thereof (other than a holder which is an "affiliate" of the Company within the meaning of Rule 405 under the Securities Act or a "broker" or "dealer" registered under the Securities Exchange Act of 1934, as amended (the "Exchange Act")), without compliance with the registration and prospectus delivery provisions of the Securities Act, provided that such Exchange Notes are acquired in the ordinary course of such holder's business and such holder is not engaging, does not intend to engage, and has no arrangement or understanding with any person to participate, in the distribution of such Exchange Notes. See "Shearman & Sterling," SEC No-Action Letter (available July 2, 1993), "Morgan Stanley & Co., Inc.," SEC No-Action Letter (available June 5, 1991) and "Exxon Capital Holding Corporation," SEC No-Action Letter (available May 13, 1988).

        The Exchange Offer is not conditioned on any minimum aggregate principal amount of Original Notes being tendered, except that Original Notes may be tendered only in an aggregate principal amount of $100,000 and integral multiples of $1,000 in excess thereof.

        Notwithstanding any other provisions of the Exchange Offer, or any extension of the Exchange Offer, the Company will not be required to accept for exchange, or to exchange any Exchange Notes for, any Original Notes and may terminate the Exchange Offer (whether or not any Original Notes have been accepted for exchange) or may waive any conditions to or amend the Exchange Offer, if any of the conditions described in the Prospectus under "The Exchange Offer—Conditions of the Exchange Offer" have occurred or exist or have not been satisfied.

        For your information and for forwarding to your clients for whom you hold Original Notes registered in your name or in the name of your nominee, we are enclosing the following documents:

1.
A Prospectus, dated                        , 2002.

2.
A Letter of Transmittal for your use and for the information of your clients.

3.
A printed form of letter which may be sent to your clients for whose accounts you hold Original Notes registered in your name or in the name of your nominee, with space provided for obtaining such clients' instructions with regard to the Exchange Offer.

4.
Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9 of the Internal Revenue Service (included in the Letter of Transmittal after the instructions thereto).

        WE URGE YOU TO CONTACT YOUR CLIENTS AS PROMPTLY AS POSSIBLE.

        Any inquiries you may have with respect to the Exchange Offer may be addressed to, and additional copies of the enclosed materials may be obtained from, the Exchange Agent at the following telephone number: (212) 815-6331.

Very truly yours,

Aon Corporation

        NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU AS THE AGENT OF THE COMPANY, THE EXCHANGE AGENT OR ANY OTHER PERSON, OR AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY DOCUMENT OR MAKE ANY STATEMENT ON BEHALF OF ANY OF THEM IN CONNECTION WITH THE EXCHANGE OFFER OTHER THAN THE DOCUMENTS ENCLOSED HEREWITH AND THE STATEMENTS CONTAINED THEREIN.

2

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Exhibit 99.3

EX-99.4 12 a2086409zex-99_4.htm EX 99.4
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Exhibit 99.4

AON CORPORATION

OFFER TO EXCHANGE
Its
6.20% Notes due 2007
Which Have Been Registered Under the Securities Act of 1933
for Any and All of Its Outstanding
6.20% Notes due 2007

                        , 2002

To Our Clients:

        Enclosed for your consideration are the Prospectus, dated                        , 2002 (as the same may be amended and supplemented from time to time, the "Prospectus"), and the related Letter of Transmittal (which together with the Prospectus constitute the "Exchange Offer"), in connection with the offer by Aon Corporation, a Delaware corporation (the "Company"), to exchange the Company's 6.20% Notes due 2007 (the "Exchange Notes") which have been registered under the Securities Act of 1933, as amended (the "Securities Act"), for any and all of the Company's outstanding 6.20% Notes due 2007 (the "Original Notes"), upon the terms and subject to the conditions set forth in the Exchange Offer. The Exchange Offer will expire at 5:00 p.m., New York City time, on                        , 2002, unless extended (the "Expiration Date").

        We are holding Original Notes for your account. An exchange of the Original Notes can be made only by us and pursuant to your instructions. The Letter of Transmittal is furnished to you for your information only and cannot be used by you to exchange the Original Notes held by us for your account. The Exchange Offer provides a procedure for holders to tender by means of guaranteed delivery.

        We request information as to whether you wish us to exchange any or all of the Original Notes held by us for your account upon the terms and subject to the conditions of the Exchange Offer.

        Your attention is directed to the following:

1.
The forms and terms of the Exchange Notes are the same in all material respects as the forms and terms of the Original Notes (which they replace), except that the Exchange Notes have been registered under the Securities Act. Interest on the Exchange Notes will accrue from the most recent January 15 or July 15 on which interest was paid or provided for on the Original Notes.

2.
Based on an interpretation by the staff of the Division of Corporation Finance of the Securities and Exchange Commission (the "SEC"), as set forth in certain interpretive letters addressed to third parties in other transactions, Exchange Notes issued pursuant to the Exchange Offer in exchange for Original Notes may be offered for resale, resold and otherwise transferred by a holder thereof (other than a holder which is an "affiliate" of the Company within the meaning of Rule 405 under the Securities Act or a "broker" or "dealer" registered under the Securities Exchange Act of 1934, as amended (the "Exchange Act")) without compliance with the registration and prospectus delivery provisions of the Securities Act, provided that such Exchange Notes are acquired in the ordinary course of such holder's business and such holder is not engaging, does not intend to engage, and has no arrangement or understanding with any person to participate, in the distribution of such Exchange Notes. See "Shearman & Sterling," SEC No-Action Letter (available July 2, 1993), "Morgan Stanley & Co., Inc.," SEC No-Action Letter (available June 5, 1991) and "Exxon Capital Holdings Corporation," SEC No-Action Letter (available May 13, 1988).

3.
The Exchange Offer is not conditioned on any minimum aggregate principal amount of Original Notes being tendered. The Exchange Notes will be exchanged for the Original Notes at the rate of $1,000 principal amount of Exchange Notes for $1,000 principal amount of Original Notes.

4.
Notwithstanding any other provisions of the Exchange Offer, or any extension of the Exchange Offer, the Company will not be required to accept for exchange, or to exchange any Exchange Notes for, any Original Notes and may terminate the Exchange Offer (whether or not any Original Notes have been accepted for exchange) or may waive any conditions to or amend the Exchange Offer, if any of the conditions described in the Prospectus under "The Exchange Offer—Conditions of the Exchange Offer" have occurred or exist or have not been satisfied.

5.
Tendered Original Notes may be withdrawn at any time prior to 5:00 p.m., New York City time, on the Expiration Date, if such Original Notes have not previously been accepted for exchange pursuant to the Exchange Offer.

6.
Any transfer taxes applicable to the exchange of Original Notes pursuant to the Exchange Offer will be paid by the Company, except as otherwise provided in Instruction 9 of the Letter of Transmittal.

        If you wish to have us tender any or all of your Original Notes, please so instruct us by completing, detaching and returning to us the instruction form attached hereto. An envelope to return your instructions is enclosed. If you authorize a tender of your Original Notes, the entire principal amount of Original Notes held for your account will be tendered unless otherwise specified on the instruction form. Your instructions should be forwarded to us in ample time to permit us to submit a tender on your behalf by the Expiration Date.

        The Exchange Offer is not being made to, nor will tenders be accepted from or on behalf of, holders of the Original Notes in any jurisdiction in which the making of the Exchange Offer or acceptance thereof would not be in compliance with the laws of such jurisdiction or would otherwise not be in compliance with any provision of any applicable securities law.

2

AON CORPORATION

OFFER TO EXCHANGE
Its
6.20% Notes due 2007
Which Have Been Registered Under the Securities Act of 1933
for Any and All of Its Outstanding
6.20% Notes due 2007

Instructions from Beneficial Owner

        The undersigned acknowledge(s) receipt of your letter and the enclosed Prospectus and the related Letter of Transmittal in connection with the offer by the Company to exchange Exchange Notes for Original Notes.

        This will instruct you to tender the principal amount of Original Notes indicated below held by you for the account of the undersigned, upon the terms and subject to the conditions set forth in the Prospectus and the related Letter of Transmittal.

        The undersigned represents that (i) the Exchange Notes acquired pursuant to the Exchange Offer are being obtained in the ordinary course of the undersigned's business, (ii) the undersigned is not engaging, does not intend to engage, and has no arrangement or understanding with any person to participate, in the distribution of such Exchange Notes, (iii) the undersigned is not an "affiliate," as defined under Rule 405 of the Securities Act, of the Company and (iv) the undersigned is not a "broker" or "dealer" who acquired Original Notes for its own account pursuant to market-making or other trading activities.

Sign Here


Signature(s)

3

Securities which are to be tendered:

Tender all of the Original Notes

Aggregate Principal Amount*

o Original Notes


Name(s) (Please Print)


Address


Zip Code


Area Code and Telephone No.

Dated:                                                  , 2002




*
Unless otherwise indicated, it will be assumed that all of the Original Notes listed are to be tendered.

4

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Exhibit 99.4

~~-----END PRIVACY-ENHANCED MESSAGE-----~~

o		CHECK HERE IF CERTIFICATES REPRESENTING THE TENDERED ORIGINAL NOTES ARE ENCLOSED WITH THIS LETTER OF TRANSMITTAL.
o		CHECK HERE IF TENDERED ORIGINAL NOTES ARE BEING DELIVERED BY BOOK-ENTRY TRANSFER TO THE ACCOUNT MAINTAINED BY THE EXCHANGE AGENT WITH DTC AND COMPLETE THE FOLLOWING:


Name(s) and address(es) of registered holder(s), exactly as name(s) appear(s) on Original Notes, or on a security position	Certificate number(s) of Original Notes*	Aggregate principal amount represented by certificate(s)	Aggregate principal amount tendered**

		Name:
		Address:
		(Include Zip Code)
		(Tax Identification or Social Security Number)

o		Credit Exchange Notes or unexchanged Original Notes delivered by book-entry transfer to the DTC account set forth below:


SIGNATURE OF REGISTERED HOLDER(S) OR AUTHORIZED SIGNATORY (SEE GUARANTEE REQUIREMENT BELOW)
Dated
Name(s)
(Please Print)


Social Security Number(s) OR Federal Employer Identification Number(s)

NOTE:		FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN A $50 PENALTY IMPOSED BY THE INTERNAL REVENUE SERVICE AND BACKUP WITHHOLDING OF 31% OF ANY PAYMENTS MADE TO YOU PURSUANT TO AN OFFER. PLEASE REVIEW THE ENCLOSED GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION NUMBER ON SUBSTITUTE FORM W-9 FOR ADDITIONAL DETAILS.
NOTE:		YOU MUST COMPLETE THE FOLLOWING CERTIFICATE IF YOU CHECKED THE BOX IN PART 3 OF THE SUBSTITUTE FORM W-9.

Firm		Authorized Signature
Address	Name	(Please Type or Print)
Zip Code	Title
	Dated		, 2002

Aggregate Principal Amount*
o Original Notes
Name(s) (Please Print)
Address
Zip Code
Area Code and Telephone No.
Dated: , 2002