OBJECTIVE: This paper reports on the sexual health knowledge and risk behaviours of year 10 and 12 students between 1997 and 2008. METHOD: Data were from nationally representative cross-sectional stratified cluster samples of year 10 and 12 students in the Australian secondary school system collected at three intervals--1997, 2002 and 2008. A number of methods were used to analyse students' sexual health knowledge and behavioural data over time. RESULTS: Student knowledge of HIV/AIDS has stabilised since the 2002 survey and remains high. Between 1997 and 2008 there has been an increase in student knowledge with respect to STIs and hepatitis. Although the proportion of students reporting ever having had sexual intercourse has increased over time, the increases between 2002 and 2008 were not significant. There has been a significant increase in the number of sexual partnerships reported by students over a year, particularly for those in year 12. CONCLUSION: Student knowledge of HIV/AIDS remains high and there has been some improvement in STI and hepatitis knowledge, although knowledge in these domains is still moderate. Sexually active students were more likely to report having sex with multiple partners compared to previous surveys. Consistency of condom use has not increased since 1997. IMPLICATIONS: Although consistent condom use remains moderately high, it is of some concern that condom use has not increased since 1997 despite related increases in sexual activity among adolescents who have experienced sexual intercourse and increased rates of STIs among this group.