This study examined sexual risk behavior and mental health in 605 HIV-positive MSM to see if men in primary partnerships had lower levels of sexual risk behavior and less depression and anxiety, compared to single men. Results. Monogamy status and partner type were associated with differences in sexual risk behavior. When non-monogamous men engaged in sex with their primary partners, their sexual risk behavior was lower, similar to monogamous men. In contrast, when these same non-monogamous men engaged in sex with their secondary partners, their sexual risk behavior was significantly higher, similar to sexually active single men. No association was found related to mental health. Conclusions. Non-monogamous men engaged in more sexual risk behavior than monogamous men due to higher rates of unsafe sex with secondary partners. Lower sexual risk behavior was only apparent when sexual behavior occurred between primary partners. This protective health benefit was not apparent when sexual behavior occurred with secondary partners.