Exhibit 15




Board of Directors and Stockholders
Aon Corporation


We are aware of the incorporation by reference in the Registration Statements of
Aon  Corporation  ("Aon")  described in the following  table of our report dated
August  10,  2000  relating  to the  unaudited  condensed  consolidated  interim
financial  statements of Aon Corporation  that are included in its Form 10-Q for
the quarter ended June 30, 2000:

    Registration Statement
    ----------------------
      Form      Number                    Purpose
      ----      ------                    -------

      S-8      33-27984    Pertaining to Aon's savings plan
      S-8      33-42575    Pertaining  to  Aon's  stock  award  plan  and  stock
                              option plan
      S-8      33-59037    Pertaining  to  Aon's  stock  award  plan  and  stock
                              option plan
      S-4      333-21237   Offer to exchange Capital Securities of Aon Capital A
      S-3      333-50607   Pertaining to the  registration  of 369,000 shares of
                              common stock
      S-8      333-55773   Pertaining  to Aon's stock award plan,  stock  option
                              plan and employee stock purchase plan
      S-3      333-78723   Pertaining to the  registration  of debt  securities,
                              preferred stock  and common stock

Pursuant to Rule 436(c) of the  Securities Act of 1933, our report is not a part
of the registration  statements  prepared or certified by accountants within the
meaning of Section 7 or 11 of the Securities Act of 1933.

                                                           /s/ ERNST & YOUNG LLP
                                                           ---------------------
                                                            ERNST & YOUNG LLP



Chicago, Illinois
August 10, 2000