SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No.    )

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Filed by a Party other than the Registrant    ¨

Check the appropriate box:

¨ Preliminary Proxy Statement

¨ Confidential, for Use of the Commission Only (as Permitted by Rule 14a-6(e)(2))

¨ Definitive Proxy Statement

x Definitive Additional Materials

¨ Soliciting Material Pursuant to §240.14a-11(c) or §240.14a-12

Costco Wholesale Corporation

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

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x No fee required.

¨ Fee computed on table below per Exchange Act Rules 14a(6)(i)(4) and 0-11.

(1) Title of each class of securities to which transaction applies:                                                                        

(2) Aggregate number of securities to which transaction applies:                                                                       

(3) Per unit price or other underlying value of transaction computed pursuant to Exchange Act Rule 0-11 (Set forth the amount on which the filing fee is calculated and state how it was determined):

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¨ Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

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*** Exercise Your Right to Vote ***

Important Notice Regarding the Availability of Proxy Materials for the Shareholder Meeting to Be Held on January 24, 2013

COSTCO WHOLESALE CORPORATION

COSTCO WHOLESALE CORPORATION 999 LAKE DRIVE

ISSAQUAH, WA 98027

Meeting Information

Meeting Type: Annual Meeting

For holders as of: November 23, 2012

Date: January 24, 2013

Time: 4:00 PM PST

Location: Meydenbauer Center

Center Hall

11100 NE 6th Street

Bellevue, Washington 98004

You are receiving this communication because you hold shares in the above named company.

This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side).

We encourage you to access and review all of the important information contained in the proxy materials before voting.

See the reverse side of this notice to obtain proxy materials and voting instructions.

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Before You Vote

How to Access the Proxy Materials

Proxy Materials Available to VIEW or RECEIVE:

1. Annual Report 2. Notice & Proxy Statement

How to View Online:

Have the information that is printed in the box marked by the arrow XXXX XXXX XXXX (located on the following page) and visit: www.proxyvote.com.

How to Request and Receive a PAPER or E-MAIL Copy:

If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request:

1) BY INTERNET: www.proxyvote.com

2) BY TELEPHONE: 1-800-579-1639

3) BY E-MAIL*: sendmaterial@proxyvote.com

* If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow XXXX XXXX XXXX (located on the following page) in the subject line.

Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before January 10, 2013 to facilitate timely delivery.

How To Vote

Please Choose One of the Following Voting Methods

Vote In Person: Many shareholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares.

Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow XXXX XXXX XXXX available and follow the instructions.

Vote By Mail: You can vote by mail by requesting a paper copy of the materials, which will include a proxy card.

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Voting items

The Board of Directors recommends you vote FOR the following:

1. Election of Directors

Nominees

01 Benjamin S. Carson, Sr. 02 William H. Gates 03 Hamilton E. James 04 W. Craig Jelinek 05 Jill S. Ruckelshaus

The Board of Directors recommends you vote FOR proposals 2 and 3.

2 Ratification of selection of independent auditors.

3 Approval, on an advisory basis, of executive compensation.

The Board of Directors recommends you vote AGAINST the following proposal:

4 Consideration of shareholder proposal to eliminate the classification of the Board of Directors.

NOTE: Such other business as may properly come before the meeting or any adjournment thereof.

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