This study describes psychological and behavioral differences between gay men in primary relationships and single men from 1985 through 1989. In addition, differences in sexual behavior, relationship status, and relationship quality between HIV positive and HIV negative men were investigated. Data are from the San Francisco Men's Health Study and included only men who were gay identified and who participated in the longitudinal surveys in 1985, 1987 and 1989 (N = 452). Participants were stratified by relationship status and by HIV status. HIV positive men were less likely than HIV negative men to be in primary relationships (38.9% vs. 52.9%, respectively in 1989). In addition, men in relationships had higher rates of unprotected anal intercourse than single men (32.6% vs. 17.0%, respectively in 1989). Differences in psychosocial and behavioral variables were found and have considerable implications for prevention programs and mental health services trying to meet the needs of the gay men's community.