OBJECTIVE: To describe the prevalence and determinants of HIV stigma in 21 communities in Zambia and South Africa. DESIGN: Analysis of baseline data from the HPTN 071 (PopART) cluster-randomized trial. HIV stigma data came from a random sample of 3859 people living with HIV. Community-level exposures reflecting HIV fears and judgements and perceptions of HIV stigma came from a random sample of community members not living with HIV (n = 5088), and from health workers (HW) (n = 851). METHODS: We calculated the prevalence of internalized stigma, and stigma experienced in the community or in a healthcare setting in the past year. We conducted risk-factor analyses using logistic regression, adjusting for clustering. RESULTS: Internalized stigma (868/3859, prevalence 22.5%) was not associated with sociodemographic characteristics but was less common among those with a longer period since diagnosis (P = 0.043). Stigma experienced in the community (853/3859, 22.1%) was more common among women (P = 0.016), older (P = 0.011) and unmarried (P = 0.009) individuals, those who had disclosed to others (P < 0.001), and those with more lifetime sexual partners (P < 0.001). Stigma experienced in a healthcare setting (280/3859, 7.3%) was more common among women (P = 0.019) and those reporting more lifetime sexual partners (P = 0.001) and higher wealth (P = 0.003). Experienced stigma was more common in clusters wherever community members perceived higher levels of stigma, but was not associated with the beliefs of community members or HW. CONCLUSION: HIV stigma remains unacceptably high in South Africa and Zambia and may act as barrier to HIV prevention and treatment. Further research is needed to understand its determinants.