This study investigated the attitudes of 43 teachers and school administrators towards sex education, young people's sexuality and their communities in 19 secondary schools in rural KwaZulu-Natal, South Africa, and how these attitudes affect school-based HIV prevention and sex education. In interviews, teachers expressed judgemental attitudes towards young people's sexuality and pregnant students, and focused on girls' perceived irresponsible behaviour instead of strategies to minimise HIV risk. Despite general awareness of the HIV epidemic, few teachers perceived it as an immediate threat, and teachers' own HIV risk was infrequently acknowledged. Teachers perceived themselves to have higher personal standards and moral authority than members of the communities and schools they served. Male administrators' authority to determine school policies and teachers' attitudes towards sexuality fundamentally affect the content and delivery of school-based sexuality education and HIV prevention activities. Opportunities to create a supportive educational environment for students and for female teachers are frequently missed. Improving teachers' efficacy to deliver impartial, non-judgemental and accurate information about sex and HIV is essential, as are efforts to acknowledge and address their own HIV risks. (Contains 1 table.)