The precise manner in which the use of different types of drugs is related to prostitution has not been adequately researched. This study investigates patterns of drug-taking and sexual behaviour among a group of women working as prostitutes in south London; it also looks at prostitution in which sex is offered in return for drugs, at the links between heroin, cocaine and alcohol use and sexual behaviour, and at the association between severity of dependence and sexual behaviour. All of the women in our sample (n = 51) were actively working as prostitutes. More than half of them had given sex for drugs, though this was a relatively infrequent occurrence. The majority of them were using heroin and many of them were moderately or severely dependent upon heroin. More than one-third had shared injecting equipment after it had already been used. Almost two-thirds reported that they only worked as a prostitute in order to fund their use of drugs (predominantly heroin), and that they would not continue working as a prostitute if they were not still using drugs. The more severely dependent upon heroin they were, the more likely they were to report these links between heroin use and prostitution. About half of the women in our sample said that they first started to work as a prostitute in order to pay for drugs. The women who began to use heroin prior to prostitution were more severely dependent on heroin and described themselves as being trapped in prostitution by the need to maintain a supply of heroin. Very few women regularly used cocaine in association with their prostitution. There are grounds for concern about the alcohol consumption of these women. About one-quarter of the women said that they used alcohol every day; some of them reported drinking at levels which greatly exceed recommended limits for women, and some were drinking at levels which were likely to be physically damaging.