In the spring of 1991, a survey was carried out in the "open" drug scene in Zürich's Platzspitz area with the objective of studying drug users' behaviour with regard to relationships and sexuality, a random sample of 654 users (both male and female) of illegal drugs being interviewed and the data drawn from these interviews being compared with corresponding data on average young adults aged 17 to 30. The latter data have been continuously collected since 1986 to evaluate Switzerland's strategy to prevent AIDS. About fifty per cent of drug users are in steady relationships, which is a smaller proportion than among average young adults. On the other hand, occasional sexual contacts (whether or not a steady relationship exists) are three times as frequent among drug users. The use of condoms is slightly more frequent here than among the average population, but is not as yet-and especially among those who are HIV-positive-consistent enough by any means. The influence of drug abuse on sexuality is usually felt to be negative (decline in libidinal energy, impotence), and often brings about a decrease in sexual contacts. This is equally true of both opiates and stimulants (cocaine, amphetamine). Promiscuous behaviour is rare as such and does not occur with any greater frequency than among the average population. However, a large proportion of drug users is at some stage exposed to prostitution. In summary, one can say that the preventive strategy continues to be deficient where the sexual activities of drug users are concerned. A greater effort should be made, in this context, to target the following groups: persons already frequenting advice centers, persons who are HIV-positive, and male prostitutes.