21.04.2005 – 19:05

Aon Corporation

Aon Corporation Announces First Quarter 2005 Earnings Release and Conference Call Dates

Chicago (ots/PRNewswire)

Aon Corporation (NYSE: AOC) will report
its first quarter results after the market closes on Tuesday, May 3,
2005. The earnings release will be available on Aon's web site at
http://www.aon.com .

Gregory C. Case, president and CEO, will host a webcast discussion
of the quarter's results on Wednesday, May 4, 2005 at 10:00 AM
Central Time which will be broadcast live through Aon's website at
http://www.aon.com . Windows Media Player is required to listen to
this webcast. A replay will be available shortly after the live
webcast.

Aon Corporation ( http://www.aon.com ) is a leading provider of
risk management services, insurance and reinsurance brokerage, human
capital and management consulting, and specialty insurance
underwriting. The company employs approximately 48,000 professionals
in its 500 offices in more than 120 countries. Backed by broad
resources, industry knowledge and technical expertise, Aon
professionals help a wide range of clients develop effective risk
management and workforce productivity solutions.

    Investor Contact:   Craig Streem
                        Corporate Vice President, Investor Relations
                        +1-312-381-3983
    Media Contact:      Gary Sullivan
                        Senior Vice President, Corporate Communications
                        +1-312-381-2467

Web site: http://www.aon.com

Contact:

Investors, Craig Streem, Corporate Vice President, Investor
Relations, +1-312-381-3983, or Media, Gary Sullivan, Senior Vice
President, Corporate Communications, +1-312-381-2467, both of Aon
Corporation