Stigma surrounding HIV/AIDS has existed since the beginning of the epidemic, but little is known about HIV/AIDS stigma within the gay community and how it affects men who have sex with men (MSM) living with HIV. A better understanding of the effects of stigma on this population is needed to reduce it and its harmful effects. Our study used quantitative data from 206 HIV-positive MSM and qualitative data from 250 to document beliefs about HIV/AIDS stigma within the gay community and to measure its effects on sexual risk behaviors, substance use behaviors, serostatus disclosure, and mental health. Stigma was associated with increased levels of anxiety, loneliness, depressive symptoms, engaging in avoidant coping strategies, and history of suicidal ideation. HIV/AIDS stigma exists within the gay community and has a negative effect on the mental health of people living with HIV. HIV/AIDS stigma should be monitored closely so that we may better understand how to address it.