Income slipped at Aon despite revenues increasing in the first quarter compared to last year.
Net income was $152m (£94m) compared to $160m (£99.3m) a year ago.
Earnings per share were 48 cents against 57 cents.
Revenues grew 14% to $2.4bn (£1.5bn)from $2.1bn (£1.3bn).
Factors depressing income included a $37m (£23m) pre-tax WTC charge resulting from the broker's need to rent temporary office space in Manhattan after the attacks.