Repeated cross-sectional surveys have been conducted to collect information on the trend of HIV prevalence among drug users attending drug treatment centers in Italy in the years 1990-92. Annual HIV prevalence was 31.5% in 1990, 29.1% in 1991, and 24.6% in 1992, showing a declining trend. HIV prevalence was higher in the North than in the South of the country, and among females than in males. Drug users entering treatment for the first time during the study period were less likely to be infected than old clients.