China is currently undergoing a serious HIV-1 epidemic in intravenous drug users, sex workers, and former plasma donors. Little is known, however, about HIV-1 risk in Chinese men who have sex with men. In this study of seroprevalence in such men in Beijing, we recorded 15 (3.1%, 95% CI 1.8-5.1) of 481 men infected with HIV-1. Overall, 238 (49%) of participants reported unprotected anal intercourse during the previous 6 months. HIV-1 seropositivity was independently associated with being older than 39 years and having had more than 20 male sexual partners. Most men older than 39 years had been married. Our findings suggest the potential for spread of HIV-1 between men who have sex with men and to their heterosexual partners.