This study analysed the level of adherence to anti-HIV therapies in illegal drug users compared to non-users. Out of 214 patients interviewed. 60 (28%) reported current use of one or more illegal drugs (heroin, cocaine), alcohol (>6 U/day), psychoactive drugs and others. Within the two groups reporting use of heroin and cocaine, the percentage of patients achieving good levels of compliance was higher than among patients who reported not using any substance (50 and 46% vs. 42.3%), among the users of psychoactive pharmaceuticals and alcohol the percentage of high-compliant patients tended to be lower (respectively 26.6 and 30%), but the difference was not significant.