The HIV epidemic is fuelled by heterosexual transmission. Lesotho has an exceptionally high number of multiple and concurrent partnerships before and during marriages. Casual sex has an important contribution to new infections (65%) but also 23% of new infections are through long term or marital partners, so prevention efforts need to target high levels of multiple concurrent partnerships as well as unprotected sex in long term partnerships. Prevention needs to be targeted to adults, married couples and people in long-term steady relationships. Male circumcision is fairly low in Lesotho (15%) which is also a key driver.