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 May
4, 1999  relating to the  unaudited  condensed  consolidated  interim  financial
statements of Aon Corporation that are included in its Form 10-Q for the quarter
ended March 31, 1999:

    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-8      333-55773   Pertaining to Aon's stock award plan,  stock option
                              plan and employee stock purchase 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

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
May 4, 1999