Background This study sought to test associations between early sexual debut (first vaginal intercourse before age 15) and later sexual risk-taking among adolescents aged 15 to 19.

Methods Self-report surveys were administered to 433 high school students in Yarmouth, Nova Scotia, Canada in May 2009. The surveys asked about general demographics, socio-economic status, substance use, depression, peers' attitudes towards sex, and the sexual behaviours of students. Categorical principal components analysis was used to determine whether several of the outcome variables could be combined, and logistic regressions were used to assess the associations between predictor and outcome variables.

Results Two factors emerged among the risk behaviours: i) recreational sex (having many sexual partners, having sex while using substances and having casual partners); and; ii) inconsistent condom use, each of which was predicted by a distinct set of variables. Adjusted logistic regressions revealed that early sexual debut was associated with an increased risk of having used condoms inconsistently in the last year (OR 4.7; 95% CI 1.0 to 21.5) and having had recreational sex in the same period (OR 2.5; 95% CI 0.1.0 to 6.4) among girls. The association between early debut and sexual risk behaviours was not seen in boys.

Conclusions Early sexual debut predicted of sexual risk taking among girls but not boys. Our findings offer a partial replication and expansion on recent research examining this issue. Asking high school students about age of their sexual debut and other factors might allow healthcare professionals to identify high risk individuals.