The study examined South African adolescents' beliefs and attitudes regarding drug use, sexual risk behaviour and relationships between the two behaviours. Eleven single-gender focus groups were held among male and female Grade 8 and 11 students from three schools in Cape Town. The adolescents' opined that drugs' reinforcing effects were the main factor underlying their use, and that sexual risk behaviours resulted from girls' limited power in sexual relationships and boys' perceived invulnerability to HIV infection and the positive status associated with having multiple partners. Drug use was considered to exacerbate underlying vulnerabilities to risky sexual behaviour mainly due to drugs' effects on adolescents' inhibitions, rational thinking, and safer sex negotiation skills. The findings suggest that adolescent HIV intervention programmes should address the risks posed by drug use on sexual behaviour.