Two surveys were conducted in 1990 and 1991 in order to estimate the prevalence of HIV infection among injecting drug users attending drug treatment centers throughout Italy. Among the 35,073 IDUs attending these facilities in 1990, 32.1% were HIV-positive. In 1991, 29.7% of 41,794 IDUs were HIV-positive. HIV prevalence was higher among prior attendees compared to new entrants (38.0% vs. 20.5% in 1990, and 35.8% vs. 16.6% in 1991); prevalence was also higher among females. These findings suggest that HIV prevalence among Italian drug users is slowly declining.