Ace reported a net loss for the third quarter, hit by a $406m loss from hurricanes and typhoons and the impact of the Eliot Spitzer probe into Marsh & McLennan.
The third-quarter net loss for Ace was $3m, compared with net income of $355m a year earlier.
Chief executive Evan Greenberg said the quarter was perhaps the worst on record for natural catastrophe losses in the property/casualty industry.
"It was a difficult financial quarter for the property/casualty industry, and Ace was no exception," he said.
Ace Global Markets, the London-based Lloyd's excess and surplus business, saw net premiums written fall 7% to $236m.
Greenberg said the drop showed "responsible underwriting" as competitive conditions made some business less attractive to Ace.
