Credit Suisse had already warned it expected to report losses
Credit Suisse has reported a loss for the first three months of the year, hit by its exposure to the credit markets.
The bank made a net loss of 2.1bn Swiss francs ($2.1bn; £1.0bn) after writing down 5.3bn Swiss francs in mortgage securities and big buyout loans.
It had made a net profit of 2.7bn Swiss francs in the same period of last year.
Credit Suisse had already warned it was likely to make a loss, which it blamed partly on the "intentional misconduct" of a number of traders.
Credit Suisse wrote down £850m on leverage finance such as loans to finance private-equity deals, and a further £400m on commercial mortgages.
"It is further confirmation that imprudent lending and investing was not confined to US subprime and collateralised debt obligations," said BBC's business editor, Robert Peston.
"The inevitable hangover has arrived following the frenzied obsession to do private deals at almost any price in 2006 and 2007," he said.
Credit Suisse reported that conditions had improved in April but stressed it was not counting on an upturn yet and that there may be further write-downs to come.
"In this crisis, a number of times people have seen a light at the end of the tunnel and it has ended up being a train coming down the tracks," said Brady Dougan, chief executive of Credit Suisse.
Switzerland's second biggest bank's losses from the credit crisis are tiny compared with those of its bigger compatriot UBS, which has so far made $37.4bn of losses.