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                                                                     Exhibit 15

November 11, 2002

Board of Directors and Stockholders
Aon Corporation

We are aware of the incorporation by reference in the Registration Statement
(Amendment No. 1 to Form S-4 333-100464) of Aon Corporation of our reports
dated April 29, 2002 (except for Note 2, as to which the date is August 14,
2002), August 14, 2002 and November 11, 2002 relating to the unaudited
condensed consolidated interim financial statements of Aon Corporation which
are included in its Form 10-Q/A for the quarter ended March 31, 2002 and Form
10-Q for the quarters ended June 30, 2002 and September 30, 2002.

                                          /s/ ERNST & YOUNG LLP