A cross-sectional study was undertaken on the correlates of infection for the human immunodeficiency virus (HIV) and hepatitis viruses B and C (HBV and HCV) in a sample of inmates from eight Italian prisons. A total of 973 inmates were enrolled [87.0% males, median age of 36 years, 30.4% intravenous drug users (IDUs), 0.6% men who have sex with men (MSWM)]. In this sample, high seroprevalence rates were found (HIV: 7.5%; HCV: 38.0%; anti-HBc: 52.7%; HBsAg: 6.7%). HIV and HCV seropositivity were associated strongly with intravenous drug use (OR: 5.9 for HIV; 10.5 for HCV); after excluding IDUs and male homosexuals, the HIV prevalence remained nonetheless relatively high (2.6%). HIV prevalence was higher for persons from Northern Italy and Sardinia. The age effect was U-shaped for HIV and HCV infections; HBV prevalence increased with age. Tattoos were associated with HCV positivity (OR: 2.9). The number of imprisonments was associated with HIV infection, whereas the duration of imprisonment was only associated with anti-HBc. The probability of being HIV-seropositive was higher for HCV-seropositive individuals, especially if IDUs. In conclusion, a high prevalence of HIV, HCV, and HBV infections among inmates was observed: these high rates are in part attributable to the high proportion of IDUs. Frequency of imprisonment and tattoos were associated, respectively, with HIV and HCV positivity. Although it is possible that the study population is not representative of Italy's prison inmate population, the results stress the need to improve infection control measures users was prisons.