Since January 1987 a study of HIV prevalence and risk behaviour among i v drug abusers at the remand prison in Stockholm has been carried out by a research team working independently of the penal system. On a voluntary basis, a standardised interview is carried out and an HIV blood test made. Of the 2,038 i v drug abusers who participated up to December 1991, ten per cent were HIV-positive. Of the 80 per cent who mainly used amphetamines, six per cent were seropositive, as compared with about 28 per cent of the remaining 20 per cent who were heroin addicts. The overall annual incidence of HIV infection was about one per cent. The cumulative prevalence decreased among heroin users during the observation period, but remained constant among amphetamine users. The frequency of injection equipment sharing showed a decline at the beginning of the observation period, but the level of sexual risk behaviour has remained high.