Objective:To determine the knowledge and attitudes of adolescents with respect to reproductive health, with particular emphasis on their knowledge of the symptoms and transmission of sexually transmitted diseases (STDs), preventive strategies and sources of information.Design:Questionnaire survey of a stratified random sample of Year 10 students followed by group interviews with volunteers from the sample.Setting:The study was carried out in 33 Victorian secondary schools.Participants:The questionnaire was administered to a stratified random sample of 1351 Year 10 students. Group interviews were conducted with 533 volunteers from the sample.Measurements and main results:Considerable gaps were identified in knowledge of STDs and their short‐term and long‐term effects on reproductive health. An STD Knowledge Score was constructed based on responses to 46 items. The mean score for the full sample was 22.7 (49.3% correct) with a standard deviation of 6.4. As a group, country students scored better than city students (mean, 23.8 v. 22.2,t= 3.97,P<0.001) and females better than males (mean, 23.5 v. 21.9,t= 4.21,P<0.001). Medical practitioners were rarely identified as a source of preventive advice.Conclusion:The deficiencies identified in knowledge about reproductive health suggest that young people need better access to health information. Schools and the medical profession need to work together both to provide information and to help young people develop the confidence to use available information sources.