Objective: This study evaluated the longitudinal impact of the Teen Outreach Programme (TOP) on adolescent pregnancy, sexual behaviour, risky sex and sexual intentions in non-metropolitan high schools. Design: Pair-matched, cluster randomised controlled trial. Setting: Non-metropolitan public high schools in Florida, USA. Methods: TOP was evaluated against the standard school health curriculum content. Young people (N = 3,836) enrolled in 26 schools were surveyed at baseline (2012), immediate post-programme (2013) and at 1-year follow-up (2014). Most youth were 14 years old and in ninth grade at baseline. Missing data were imputed using a sequential imputation procedure and analysis took place using generalised linear mixed-effects models with logit link function. Results: Post-programme, young people in the treatment group were less likely to report ever having sex, recent sex, recent sex without a condom or intention to have sex in the next year. At 1-year follow-up, programme participants were less likely to report ever having been pregnant or having got someone pregnant. When examining treatment effects by gender, statistically significant differences were found only for female programme participants. Conclusion: Although many protective factors dissipated by second follow-up and were primarily found among female programme participants, TOP has the potential to decrease risky sexual behaviour.