Early school leavers cannot access school-based sex education programmes, increasing their vulnerability to sexual health issues. This study evaluated a culturally-sensitive and target-orientated sex education programme involving this group. Early school leavers were recruited from two branches of the Chinese Young Men's Christian Association in Hong Kong. These potential peer educators (PEs) attended five three-hour workshops providing comprehensive sex and sexuality education. They then provided peers with sex education, whilst receiving continuing support and attending additional training and activities. The Safer Choice Student Health Questionnaire, Mathtech Student Course Evaluation and Student Assessment of Course Impact questionnaires and Behavioral Intent Questionnaire were used to assess attitudes towards the programme and changes in knowledge, attitudes, practices regarding sex and sexual health. Of 60 PEs, 97% completed the workshop course. Seven months post intervention, changes in attitude towards contraception (p = 0.01) and a lower likelihood of having sex (p less than 0.001) were found amongst PEs. At 14 months, PEs were less likely to have sex (p less than 0.001) and were more comfortable talking about sex with friends and family (p = 0.01) but no difference was observed in pre-training and post-training tests among 545 targeted peers. The intervention successfully engaged the heavily involved PEs, and had some positive effects on their willingness to discuss sexual health issues, their perceived likelihood of having and their attitude towards sexual intercourse. (Contains 5 tables.)