Gender-based violence (GBV) is common in southern Africa. Here we use GBV to include sexual and non-sexual physical violence, emotional abuse, and forms of child sexual abuse. A sizeable literature now links GBV and HIV infection.Sexual violence can lead to HIV infection directly, as trauma increases the risk of transmission. More importantly, GBV increases HIV risk indirectly. Victims of childhood sexual abuse are more likely to be HIV positive, and to have high risk behaviours.GBV perpetrators are at risk of HIV infection, as their victims have often been victimised before and have a high risk of infection. Including perpetrators and victims, perhaps one third of the southern African population is involved in the GBV-HIV dynamic.A randomised controlled trial of income enhancement and gender training reduced GBV and HIV risk behaviours, and a trial of a learning programme reported a non-significant reduction in HIV incidence and reduction of male risk behaviours (primary prevention). Interventions among survivors of GBV can reduce their HIV risk (secondary prevention). Various strategies can reduce spread of HIV from infected GBV survivors (tertiary prevention). Dealing with GBV could have an important effect on the HIV epidemic.A policy shift is necessary. HIV prevention policy should recognise the direct and indirect implications of GBV for HIV prevention, the importance of perpetrator dynamics, and that reduction of GBV should be part of HIV prevention programmes. Effective interventions are likely to include a structural component, and a GBV awareness component.