Levels of heterosexually transmitted HIV infection are high amongst South African youth, with one recent survey reporting levels of 18.9% amongst 17-20 year olds and 43.1% amongst 21-25 year olds. In these groups levels of knowledge about HIV are high, but perceived vulnerability and reported condom use are low. Much existing research into youth HIV in developing countries relies on survey measures which use individual knowledge, attitudes and reported behaviour as variables in seeking to explain HIV transmission amongst this group. This paper reports on a focus group study that seeks to complement existing individual-level quantitative findings with qualitative findings highlighting community and social factors that hinder condom use amongst youth in the township of Khutsong, near Carletonville. Study informants comprised 44 young women and men in the 13-25 year age group. Data analysis highlighted six factors hindering condom use: lack of perceived risk; peer norms; condom availability; adult attitudes to condoms and sex; gendered power relations and the economic context of adolescent sexuality. Informants did not constitute a homogenous group in terms of their understandings of sexuality. While there was clear evidence for the existence of dominant social norms which place young peoples' sexual health at risk, there was also evidence that many young people are self-consciously critical of the norms that govern their sexual behaviour, despite going along with them, and that they are aware of the way in which peer and gender pressures place their health at risk. There was also evidence that a minority of youth actively challenge dominant norms and behave in counter-normative and health-enhancing ways. The actively contested nature of dominant sexual norms provides a fertile starting point for peer education programmes that seek to provide the context for the collective negotiation of alternative sexual norms that do not endanger young peoples' sexual health.