Aon's stock crashed by a quarter of its value today amid fears over accounting difficulties and disappointing results.
Shares in the broking giant were down by 23% by late afternoon.
They were among the biggest losers on the New York Stock Exchange.
They fell from $21.21 to $16.39.
Its latest earnings figure, of 33 cents a share compares dismally to a previous of 56 cents a share and was dubbed the worst bottom line result in the company's history.
A survey of analysts indicated they expected Aon to make 50 cents a share.
The company admitted it may have to restate earnings after talks with regulator, the Securities and Exchange Commission over how it reported investment losses in 1999, 2000 and early 2002.
If the SEC rules that Aon must change its earlier results, pretax earnings and related earnings per share would be cut to $27m, or 6 cents per share, for 1999; $24m, or 6 cents per share, for 2000; and $5m, or 1 cent per share, for the first quarter of 2002.
