Stigma toward homosexuality plays an important role in the increased risk of acquiring or transmitting HIV among men who have sex with men (MSM). This study describes associations between three dimensions of homosexuality-related stigma (enacted, perceived and internalized) and HIV risk behaviors among HIV-negative MSM in Hanoi, Vietnam. A total of 1675 HIV-negative MSM were recruited from the baseline of a cohort study from 2017 to 2019 through respondent-driven, time-location and internet-based sampling strategies. Stigma was measured by a locally validated instrument, with a higher score indicated a higher level of stigma (from 1 to 4). Enacted stigma (mean = 2.10), perceived stigma (mean = 2.62) and internalized stigma (mean = 2.55) were found. About 25% of participants reported group sex and 6.3% reported drug use before or during group sex in the last 6 months. Enacted stigma was significantly associated with group sex (adjusted OR = 1.48
95% CI 1.20-1.84) and drug use before or during group sex (adjusted OR = 1.68
95% CI 1.19-2.36). Internalized stigma was significantly associated with group sex (adjusted OR = 1.27
95% CI 1.05-1.53) and drug use before or during group sex (adjusted OR = 1.44
95% CI 1.04-1.99). The results highlight the need for multifaced interventions at a multiple socio-ecological levels to reduce stigma toward homosexuality.