Between September 1993 and December 1995, 528 foreign individuals at risk of HIV infection attended the drug treatment centre located in the Santo Spirito Hospital in Rome, undergoing medical examination, HIV testing and counselling. The geographic distribution showed that the majority of the participants were from South America (40.0%), most of whom were transsexual sex workers (from Brazil or Columbia), and from North Africa (37.5%); all the individuals coming from Western and Eastern Europe and the USA were heroin users. The overall HIV prevalence was high (21.6%), though it varied by nationality, ranging from 5.1% among North Africans to 68.3% among Brazilian transsexuals. During the study period, 170 of the individuals returned for at least one follow-up visit. Three seroconversions occurred among the 118 initially HIV-negative immigrants who were retested, all three among the 26 HIV-negative Columbian transsexuals; the seroconversion rate within this group was 10.1 per 100 persons/years. During follow-up, there was no reduction observed in drug-related practices associated with HIV infection, yet a general increase in regular condom use was reported. The increasing number of foreign persons contacting our programme emphasizes the need for easy access to care and treatment for marginalized populations possibly engaging in behaviour at risk for HIV infection. Counselling strategies seem to be relatively effective in promoting safer sex among these population groups.