There is concern about the high prevalence of adolescent sexual health problems, such as sexually transmitted diseases (STDs) and unwanted pregnancies, that currently exist in the UK. If young people are to reduce their risk from HIV/AIDS and other STDs it is imperative, in the first instance, they know what the risks are and how they can avoid them. However, effective school-based sex education can only be delivered if there are accurate data on young people's current levels of knowledge and existing sex education needs. This paper details findings from the WHO: Health Behaviours of School-aged Children Study on the changes that have occurred between 1990 and 1994 in Scottish school-children's knowledge, attitudes and perceived educational needs in relation to HIV/AIDS. There have been significant changes in knowledge and attitudes that may affect their sexual behaviour, e.g. in their attitudes to condom use, risk of HIV/AIDS and other STDs, and also other sexual health problems, such as the risk of unwanted pregnancies and abortions. Finally, areas that require future research and recommendations for future sexual health education interventions are highlighted.