OBJECTIVE:This study used matched samples from schools in the states of Victoria, Australia and Washington, United States (US), to compare sexual behaviour in early adolescence. It was hypothesised that the contrasting dominant policy objectives of harm minimisation in Australia and abstinence in the US would result in state differences for markers of sexual risk, mirroring prior cross-national findings in substance use. METHOD:A two-stage cluster sampling approach was used to recruit students from the two states. Self-reported sexual behaviour was examined for 1,596 students in annual surveys from Grade 7 in 2002 to Grade 9 in 2004. Prevalence estimates were derived for each measure of sexual behaviour, and comparisons were made between gender groups in each state. RESULTS:State differences were found for girls' first sex, with significantly more girls in Washington than Victoria having had sex by Grade 7. By Grade 9, significantly more girls in Victoria reported sex in the last year and more sexual partners than girls in Washington. A large proportion of Grade 9 students across both states reported inconsistent contraception use. CONCLUSIONS:Contradicting the abstinence policy objective, first sex by Grade 7 was more prevalent in Washington than Victoria. Whilst sexual behaviour was more prevalent in Grade 9 in Victoria, the sexually active showed no clear cross-national differences in markers of risk such as contraception use and pregnancy outcomes. Findings demonstrate few cross-national differences in adolescent sexual behaviour despite the different policy contexts of Victoria, Australia and Washington, US.