The relation between human immunodeficiency virus (HIV), human papilloma virus (HPV) infection, sexual habits, reproductive history, and risk of cervical intraepithelial neoplasia (CIN) has been analyzed in a cross-sectional study conducted since 1986 among female former intravenous drug abusers attending for the first time to the Colposcopic Unit of the Ospedale Luigi Sacco of Milan and women consecutively admitted to the Community for Past Drug Abusers, S. Patrignano, Rimini. A total of 434 subjects entered the study; of those 128 (30%) had a diagnosis of CIN. Compared with HIV-negative subjects, odds ratio (OR) of CIN was 8.0 (95% confidence interval (CI) 4.6-14.1) for HIV-positive ones and the frequency of CIN 2 and 3 was higher in HIV-positive than that in HIV-negative subjects (chi 2(1), trend, 6.67, P 0.01). Compared with women without current HPV infection the OR estimate was 38.0 (95% CI 20.3-71.2) in those with current diagnosis of HPV infection. Considering HIV-positive subjects only, the frequency of CIN increased with stage of HIV infection and was higher in women with lower CD4+ values. Finally, no relation emerged between CIN risk and age, indicators of sexual habits, oral contraceptive use, parity, and history of spontaneous or induced abortions.