NEW YORK (Bloomberg) - Aon Corp., the largest insurance broker, fell the most in six months after posting a 25 percent profit drop and saying revenue from its main unit declined excluding acquisitions and currency fluctuations.

Third-quarter net income from continuing operations dropped to $117 million, or 40 cents a share, from $155 million, or 53 cents, in the same period a year earlier, the Chicago-based broker said on Friday in a statement. Income excluding some items was 65 cents a share, missing by one cent the average estimate of 14 analysts surveyed by Bloomberg.

Aon depends on commission from matching insurers from clients and has faced pressure as corporations reduce coverage amid the recession. So-called organic revenue at its brokerage unit, excluding recently purchased businesses and the effects of currency fluctuations, declined three percent, led by a drop at the Europe, Middle East and Africa unit.

The decline was "driven by impacts of both the weak economy and a soft market" for insurance rates, CEO Gregory Case said in a conference call on Thursday.

Aon fell $2.68, or 6.5 percent, to $38.51 in New York Stock Exchange composite trading. It last fell as much on May 1. The broker has dropped 16 percent this year, compared with the 15 percent increase in the Standard & Poor's 500 Index.

Commissions and fees increased 50 percent in Aon's reinsurance business to $379 million on the purchase of Benfield Group Ltd. Case bought London-based Benfield last year to expand in Europe and add to the reinsurance business. The company booked $15 million in expenses tied to the acquisition in the quarter.

"In the short-term, there is always some turmoil associated with that because it's a people-based business," said Meyer Shields, an analyst at Stifel Nicolaus & Co., in an interview before results were released.

"When there are personnel lay-offs anticipated and executed, there is some interference. Longer-term it's the right thing to do."

Aon announced a separate restructuring plan in 2007 that led to a staff reduction of more than 3,000 employees that will trim expenses by as much as $245 million this year and $467 million in 2010.

US commercial insurance rates fell 5.8 percent in the quarter, exceeding price declines in the first half of the year, the Council of Insurance Agents and Brokers said this week. Prices have fallen every quarter since 2004.

"Market conditions remain pretty challenging," Mark Dwelle, an analyst with RBC Capital Markets, said in an interview before results were released. "The soft economy is reducing the amount of insurance most people are buying.

"That has a negative impact on overall premiums for the industry."

Willis Group Holdings Inc., the world's third-largest insurance broker, said third-quarter profit more than doubled to $79 million on increased revenue from its purchase of Hilb Rogul & Hobbs Co. Marsh & McClennan Cos., ranked second, is scheduled to report earnings on November 4.