John Paulson, the billionaire money manager mired in the worst slump of his career, lost 10.5 percent in his Gold Fund this year even as the metal heads for its 11th straight annual gain, according to people familiar with the fund’s performance.

The fund, which invests in mining stocks and other gold- related securities, remains the best performer in Paulson’s $28 billion fund family this year. His Paulson Advantage Fund, which seeks to profit from corporate events such as takeovers and bankruptcies, has fallen about 35 percent. The performance numbers for the two funds are from Dec. 28, 2010, through Dec. 20, 2011, and may not reflect returns for all shareholders, said the people, who asked not to be identified because the information is private.

Armel Leslie, a spokesman for Paulson, declined to comment on the firm’s returns.

Paulson & Co., based in New York, has lost money this year on investments including Citigroup Inc., Bank of America Corp. and Sino-Forest Corp., the Chinese forestry company accused by short-seller Carson Block of overstating timberland holdings. Paulson, 56, cut the so-called net exposure in his main hedge funds to 30 percent last month and reduced bullish bets across all his funds.

Net exposure is calculated by subtracting the percentage of a hedge fund’s short positions, or bets on falling securities, from its longs, or wagers on rising stocks and bonds.

Gold BUGS Index

Gold has climbed 13 percent this year, holding onto gains after peaking at $1,891 an ounce on Aug. 22. The 17-company NYSE Arca Gold BUGS Index fell 11 percent as investors fled equities amid the turmoil caused by the European sovereign-debt crisis.

Paulson was the largest holder of American depositary receipts in AngloGold Ashanti Ltd., the third-biggest gold producer. Paulson also owned shares or ADRs of Gold Fields Ltd., NovaGold Resources Inc., Randgold Resources Ltd., Agnico-Eagle Mines Ltd., Iamgold Corp., Barrick Gold Corp. and International Tower Hill Mines Ltd.