Many studies assessing the impact of national AIDS prevention programmes on knowledge, attitudes and practices have been published world-wide. Most have found that, while general knowledge increased, there was little change in behaviour. A survey of a random sample of 50 women attending a family planning clinic in Johannesburg determined the current knowledge, attitudes and practices of these sexually active women, aged 20-29 years. All selected respondents agreed to participate and a pretested structured questionnaire was completed. Most individuals had in excess of 7 years' schooling (78.0%), were single (58.0%) and domestic workers (28.6%). The majority were aware of AIDS (88.0%), but only 13.7% felt their knowledge was adequate. Fifty-two per cent knew sexual intercourse was a mode of transmission. Many misconceptions existed, 64.0% cited toilet seats, 47.1% sharing of utensils and 70.1% donating blood as routes by which HIV infection could be acquired. Only 47.1% and 34.1%, respectively, knew that the contraceptive pill and intra-uterine contraceptive device did not protect against HIV infection. Eighty-six per cent of the women were sexually active and 8.0% admitted to currently having more than one sexual partner. None used condoms and, generally, feelings regarding condom use were negative. Most (88.6%) believed AIDS patients should be hospitalised, 68.2% said in isolation wards, and 27.3% felt that AIDS patients should not be allowed to stay in the community. The implications of these findings are discussed and certain recommendations are made.