-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 V0vsRIdM6ZJg3u6AGzBdZpeKP7JDdPuVCEoZNAWEbRTn/AKruSSgGBtsKuxambFO
 NMxA6qBI3rPK0s/I9JBvHA==

<SEC-DOCUMENT>0001179110-03-003252.txt : 20030708
<SEC-HEADER>0001179110-03-003252.hdr.sgml : 20030708
<ACCEPTANCE-DATETIME>20030708165618
ACCESSION NUMBER:		0001179110-03-003252
CONFORMED SUBMISSION TYPE:	4/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20030515
FILED AS OF DATE:		20030708

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			RYAN PATRICK G
		CENTRAL INDEX KEY:			0001145037

	FILING VALUES:
		FORM TYPE:		4/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-07933
		FILM NUMBER:		03778799

	BUSINESS ADDRESS:	
		STREET 1:		C/O RYAN ENTERPRISES
		STREET 2:		123 N WACKER DRIVE
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60606
		BUSINESS PHONE:		3127012300

ISSUER:		

	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

	BUSINESS ADDRESS:	
		STREET 1:		200 EAST RANDOLPH STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601
		BUSINESS PHONE:		3123811000

	MAIL ADDRESS:	
		STREET 1:		200 EAST RANDOLPH STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	COMBINED INTERNATIONAL CORP
		DATE OF NAME CHANGE:	19870504
</SEC-HEADER>
<DOCUMENT>
<TYPE>4/A
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4/A -
<TEXT>
<XML>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4/A</documentType>
<periodOfReport>2003-05-15</periodOfReport>
<dateOfOriginalSubmission>2003-05-19</dateOfOriginalSubmission>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000315293</issuerCik>
        <issuerName>AON CORP</issuerName>
        <issuerTradingSymbol>AOC</issuerTradingSymbol>
</issuer>
<reportingOwner><reportingOwnerId>
            <rptOwnerCik>0001145037</rptOwnerCik>
            <rptOwnerName>RYAN PATRICK G</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>Chairman and CEO</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeSecurity><securityTitle><value>Common Stock</value>
</securityTitle>
<transactionDate><value>2003-05-15</value>
</transactionDate>
<transactionCoding><transactionFormType>4</transactionFormType>
<transactionCode>F</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>27982</value>
<footnoteId id="F1"></footnoteId>
</transactionShares>
<transactionValue><value>24.82</value>
</transactionValue>
<transactionAcquiredDisposedCode><value>D</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>13148755</value>
<footnoteId id="F2"></footnoteId>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeSecurity>
<footnotes><footnote id="F1">Shares of common stock withheld by issuer for payment of withholding taxes on the conversion of phantom stock into shares of common stock.  On the reporting person's Form 4 that is being amended, this number was incorrectly reported as 64,931.</footnote>
<footnote id="F2">On the reporting person's Form 4 that is being amended, this number was incorrectly reported as 13,111,806.  The reporting person also is the indirect beneficial owner of the following securities:  365,876 by ESOP and Savings Plan; 9,951,953 by Spouse; 583,942 by Spouse as Trustee.</footnote>
</footnotes>
<ownerSignature><signatureName>/s/ Patrick G. Ryan</signatureName>
<signatureDate>2003-07-08</signatureDate>
</ownerSignature>
</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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