Sub-Saharan Africa has the highest prevalence of HIV infection globally, with new cases occurring disproportionately in adolescents. Adolescent girls, aged 12–18 years, are especially at risk; the incidence of acquiring an HIV infection is 2–3 times higher than for boys. Gender norms and power imbalances have key roles in the risk of acquiring HIV, for example by affecting adolescent condom use. In The Lancet Series on gender equality, norms, and health, we quantified the role of gender and social norms in HIV acquisition, using an approach developed for the Series. In this Comment, we explain the findings of this quantification, through additional observational and epidemiological data.