PURPOSE: To report on changes in the sexual health knowledge and sexual and risk behaviors of year 10 and 12 Australian school students between 1992 and 2002. METHODS: Surveys were administered at five yearly intervals to a total of 6781 students in 263 government secondary schools in all Australian states and territories. RESULTS: Analysis of data from the three survey administrations shows high levels of knowledge concerning human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS), but a small but consistent decline since 1992. Knowledge about sexually transmitted infections and hepatitis remains poor. In 2002, there was an increase in the number of students reporting ever having had sexual intercourse, and this was most pronounced for year 10 students. The number of young men in year 10 who reported having three or more partners had doubled since 1997 to 33%. More year 10 young women also reported having intercourse with three or more partners. Consistency of condom use has improved over time; however, 39% still report condom use only sometimes. CONCLUSION: School-based sexual health education provides a critical basis for ensuring that young people begin to experience sex safely and with an appropriate knowledge base.