Objective: To assess effects on condom use and other sexual behaviour of an HIV prevention programme at school that promotes the use of condoms with and without emergency contraception. […] Intervention: Schools were randomised to one of three arms: an HIV prevention course that promoted condom use, the same course with emergency contraception as back-up, or the existing sex education course. Self administered anonymous questionnaires were completed at baseline, four months, and 16 months. Students at intervention schools received a 30 hour course (over 15 weeks) on HIV prevention and life skills, designed in accordance with guidelines of the joint United Nations programme on HIV/AIDS. Two extra hours of education on emergency contraception were given to students in the condom promotion with contraception arm. […] Conclusion: A rigorously designed, implemented, and evaluated HIV education course based in public high schools did not reduce risk behaviour, so such courses need to be redesigned and evaluated. Addition of emergency contraception did not decrease reported condom use or increase risky sexual behaviour but did increase reported use of emergency contraception.