Research shows that gender power inequity in relationships and intimate partner violence places women at enhanced risk of HIV infection. Men who have been violent towards their partners are more likely to have HIV. Men's behaviours show a clustering of violent and risky sexual practices, suggesting important connections. This paper draws on Raewyn Connell's notion of hegemonic masculinity and reflections on emphasized femininities to argue that these sexual, and male violent, practices are rooted in and flow from cultural ideals of gender identities. The latter enables us to understand why men and women behave as they do, and the emotional and material context within which sexual behaviours are enacted. In South Africa, while gender identities show diversity, the dominant ideal of black African manhood emphasizes toughness, strength and expression of prodigious sexual success. It is a masculinity women desire; yet it is sexually risky and a barrier to men engaging with HIV treatment. Hegemonically masculine men are expected to be in control of women, and violence may be used to establish this control. Instead of resisting this, the dominant ideal of femininity embraces compliance and tolerance of violent and hurtful behaviour, including infidelity. The women partners of hegemonically masculine men are at risk of HIV because they lack control of the circumstances of sex during particularly risky encounters. They often present their acquiescence to their partners' behaviour as a trade off made to secure social or material rewards, for this ideal of femininity is upheld, not by violence per se, by a cultural system of sanctions and rewards. Thus, men and women who adopt these gender identities are following ideals with deep roots in social and cultural processes, and thus, they are models of behaviour that may be hard for individuals to critique and in which to exercise choice. Women who are materially and emotionally vulnerable are least able to risk experiencing sanctions or foregoing these rewards and thus are most vulnerable to their men folk. We argue that the goals of HIV prevention and optimizing of care can best be achieved through change in gender identities, rather than through a focus on individual sexual behaviours.