Exhibit 15
ACKNOWLEDGEMENT OF ERNST & YOUNG LLP, INDEPENDENT REGISTERED
PUBLIC ACCOUNTING FIRM
Board of Directors and Stockholders
Aon Corporation
We are aware of the incorporation by reference in the Registration Statements of Aon Corporation described in the following table of our reports dated May 3, 2004, August 4, 2004 and November 8, 2004, relating to the unaudited condensed consolidated interim financial statements of Aon Corporation that are included in its Forms 10-Q for the quarters ended March 31, 2004, June 30, 2004 and September 30, 2004.
Registration Statement |
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Form |
| Number |
| Purpose |
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S-8 |
| 33-27984 |
| Pertaining to Aon’s savings plan |
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S-8 |
| 33-42575 |
| Pertaining to Aon’s stock award plan and stock option plan |
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S-8 |
| 33-59037 |
| Pertaining to Aon’s stock award plan and stock option plan |
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S-3 |
| 333-50607 |
| Pertaining to the registration of 369,000 shares of common stock |
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S-8 |
| 333-55773 |
| Pertaining to Aon’s stock award plan, stock option plan, and employee stock purchase plan |
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S-3 |
| 333-78723 |
| Pertaining to the registration of debt securities, preferred stock and common stock |
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S-4 |
| 333-57706 |
| Pertaining to the registration of up to 3,852,184 shares of common stock |
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S-3 |
| 333-74364 |
| Pertaining to the registration of debt securities, preferred stock, common stock, share purchase contracts, and share purchase units |
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S-3 |
| 333-100466 |
| Pertaining to the registration as amended of 2,707,018 shares of common stock |
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S-3 |
| 333-102799 |
| Pertaining to the registration of senior convertible debentures and common stock |
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S-8 |
| 333-103344 |
| Pertaining to the registration of common stock |
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S-8 |
| 333-106584 |
| Pertaining to Aon’s deferred compensation plan |
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| ERNST & YOUNG LLP |
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Chicago, Illinois |
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November 8, 2004 |
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