South Africa is reported to have the largest number of people living with HIV/AIDS in the world. The present study investigated the behavioural responses of South African youth to the HIV/AIDS epidemic. A multi-stage stratified cluster sample of 2,430 youths aged 15–24 was selected, 46.9% of them males and 53.1% females. Nurses administered questionnaires to consenting youths, measuring behavioural risks and also took an oral fluid specimen for HIV antibody testing. It was found that the median age of sexual debut for both sexes was 16.5 years; most of the youths were sexually experienced with no variation by sex; sexual experience was highest among Africans living in informal urban areas; partner turnover was low and multiple partners were more common among African males living in urban informal settings; sexual frequency among sexually active youth was relatively low; secondary abstinence during the past 12 months was 24%; condom use at last sexual intercourse was high, at 52.8% for males and 47.6% for females, especially among Africans living in urban informal settings; and the majority of youths (74%) indicated that they had discussed HIV prevention with their partners during the past 12 months. These results suggest that South African youth are heeding the message to abstain, be faithful and use a condom; messages that are at the core of South Africa's HIV/AIDS prevention programme.