Washington Mutual posted a fourth-quarter loss of $1.87 billion, or $2.19 per diluted share, falling far short of Wall Street predictions.
Shares of the U.S. thrift fell as much as 6.27 percent in after-hours trade; the stock had already closed down 6.95 percent during regular market hours on the New York Stock Exchange.
A Thomson Financial analyst survey had called for a loss of $1.36 per share, on revenue of $3.51 billion.
The company attributed the loss to the $1.6 billion after-tax charge to writedown Home Loans goodwill and the higher level of provisioning stemming from the housing market weakness.
"We announced in December a series of proactive steps being taken to manage through the unprecedented market conditions that this company and others in the financial services industry face," WaMu Chairman and Chief Executive Kerry Killinger said in a news release.
Last week, it was reported that WaMu had conducted early merger talks with JPMorgan Chase.
Merrill Lynch, Lehman Bros., Citigroup and JPMorgan each reported mortgage-related financial damage this week.