Rates of sexually transmitted infections and teenage pregnancy amongst the under-16s are causing increasing concern. There is limited evidence about the sexual behaviour and sex education preferences of this age group, especially of those from Black and minority ethnic groups. This study aimed to provide data on early heterosexual risk behaviour, and to examine preferences for the content and delivery of sex and relationships education (SRE), across ethnicity, gender and school year to inform priority setting and sex education strategies. A cross-sectional study of 3334 13-17-year-olds from 10 English urban and suburban secondary schools was conducted. Multivariate analysis was performed to examine the independent effect of demographic variables on sexual experience and preferences for sex education. A number of important differences in the sexual experience and condom use of males and females across the ethnic groups were identified. Differences in preferences for the content and delivery of sex education were also identified, particularly between male and female pupils. The findings indicate the potential for quite wide variation in sexual experience and preferences within school classrooms. The challenge for educators is therefore to develop SRE curricula that are inclusive within the constraints of school teaching. (Contains 4 figures and 13 tables.)