This study assessed the effectiveness of a 17-session HIV-prevention group intervention with gay and bisexual males. Participants were aged 18 years or older, had engaged in one or more instances of unprotected sex with other males during the preceding 12 months, and had responded to local publicity for a program to assist gay and bisexual men who were having difficulty being sexually safe. Following assessment, 159 individuals were matched and assigned to receive group counseling or remain in a wait-list condition. Treatment focused on skills training in coping with high-risk situations. The intervention appeared to be more effective with exclusively gay than with bisexual men. More positive outcomes were associated with safer behavioral patterns at baseline, higher self-efficacy for safer behavior, accurate personal assessment of HIV infection risk, the absence of alcohol/drug use in association with sex, and satisfaction with social support.