Government and media education has promoted the use of condoms in an attempt to reduce the spread of the human immunodeficiency virus (HIV). Condoms have been identified, in vitro, as an effective barrier to HIV and a large heterosexual study has shown there was no transmission of infection in those couples systematically using condoms. Safer sex knowledge and practice and HIV knowledge were assessed in 584 individuals, 16-74 years old, attending a London genitourinary medicine (GUM) clinic via a self-administered, anonymous questionnaire. Over 80% were heterosexual, 64% had attended a GUM clinic before, 60% had a history of sexually transmitted infection. Over 80% were aware of the protective effect of condoms and the risks of intravenous drug use; 66% of geographical risk factors; 49% of the risks of anal sex; and 53% perceived masturbation as safer. Only 10.4% always used condoms; over 50% gave no reason for non-use. Use was not increased in higher risk respondents nor in those with good safer sex/HIV knowledge, nor was there any sex difference. Although knowledge of some aspects of safer sex was good, anal sex risks, geographical sex risks, and alternative safer sexual practices were less well known. In addition, condom use was disappointingly low, even in the presence of good safer sex knowledge, awareness of high risk behavior and despite intense media health education. As a result of this survey educational input was increased, allowing an interaction which is lacking in media campaigns, and a variety of condoms were introduced in an attempt to increase use. Re-audit will be important in assessing the effects of such changes. Pre-adolescent targeting before sexual patterns are learned may be useful. Further research into this difficult area is essential.