The prevalence of a wide range of risk-taking behaviour among high-school students in the Cape Peninsula, South Africa, was investigated. In this article, the results for sexual behaviour are presented. Cluster sampling techniques produced a sample of 7,340 students from 16 schools in the three major education departments, of whom 79.7% answered the section dealing with sexual behaviour. A self-administered questionnaire was completed in a normal school period. Estimates for each education department were weighted to produce an overall estimate. Of the sample, 17.4% indicated a previous episode of heterosexual intercourse. The median age at first intercourse was 15.1 years. The median number of partners in the previous 12 months was 1.0. The median number of weeks since the most recent coital episode was 6.6; on this episode 76.6% had known their partners for more than 7 days, while 60.5% had done something to avoid pregnancy. The most frequently used method of contraception was injectable steroids for Xhosa-speaking students and condoms for the other students. Males and Xhosa-speaking students appear to be particularly at risk for the adverse consequences of sexual activity. The HIV epidemic has increased the urgency of introducing meaningful sexuality education in South African schools.