MGIC, which competes with Radian Group PMI Group and the U.S.Government's Federal Housing Administration (FHA), posted losses throughout the financial crisis, turning in a sole quarter of profit in the second quarter of 2010.
The largest U.S. mortgage insurer's stock has dropped 19 percent this year, compared with a 2 percent fall in the broader KBW Mortgage Finance Index.
MGIC, which pays claims in case of a default or a foreclosure, said net claims paid during the first quarter increased to $687 million from $519 million a year ago.
The weak results from MGIC come even as mortgage insurers are widely expected to gain from the federal government's plans to reduce its role in propping up the mortgage market.
In February, the White House offered three broad options for overhauling a mortgage market that cratered in 2008, triggering a wave of home foreclosures and the worst banking crisis since the Great Depression.
Mortgage insurers have been battling to regain market share from the FHA, which offers lower rates and affordable down-payments to first-time buyers and controls some 80 percent of the market.
MGIC's net loss for the first quarter was $33.7 million, or 17 cents a share, compared with a net loss of $150.1 million, or $1.20 a share, in the year-ago period.
Analysts had expected the company to post a loss of 6 cents a share, according to Thomson Reuters I/B/E/S.
Milwaukee-based MGIC said investment income for the quarter fell 18 percent to $56.5 million.
The percentage of delinquent loans, excluding bulk loans, was 13.9 percent at the end of the quarter, compared with 15.4 percent a year ago.
Shares of the company closed at $8.39 on Tuesday on the New York Stock Exchange.