BACKGROUND: South African policy makers are reviewing legislation of prostitution, concerned that criminalisation hampers HIV prevention. They seek to understand the relationship between transactional sex, prostitution, and the nature of the involved men. METHODS: 1645 randomly-selected adult South African men participated in a household study, disclosing whether they had sex with a woman in prostitution or had had a provider relationship (or sex), participation in crime and violence and completing psychological measures. These became outcomes in multivariable regression models, where the former were exposure variables. RESULTS: 51% of men had had a provider relationship and expected sex in return, 3% had had sex with a woman in prostitutio...