African-Americans show worse HIV disease outcomes compared to Whites. Health disparities may be aggravated by discrimination, which is associated with worse health and maladaptive health behaviors. We examined longitudinal effects of discrimination on antiretroviral treatment adherence among 152 HIV-positive Black men who have sex with men. We measured adherence and discrimination due to HIV-serostatus, race/ethnicity, and sexual orientation at baseline and monthly for 6 months. Hierarchical repeated-measures models tested longitudinal effects of each discrimination type on adherence. Over 6 months, participants took 60% of prescribed medications on average; substantial percentages experienced discrimination (HIV-serostatus, 38%; race/ethnicity, 40%; and sexual orientation, 33%). Greater discrimination due to all three characteristics was significantly bivariately associated with lower adherence (all p's < 0.05). In the multivariate model, only racial discrimination was significant (p < 0.05). Efforts to improve HIV treatment adherence should consider the context of multiple stigmas, especially racism.