In 189 anti-HIV positive subjects (130 males and 59 females; median age 32 years, range 17-57) we evaluated the prevalence of patients with hepatitis infections, the role of parenteral and sexual risk factors on the acquisition of these infections and the reciprocal influence between HIV and HCV infections. HCV infection was detected in 53.9% of cases and HBV infection in 8.4%. In only 32% of our patients no marker of hepatitis virus infection was detected. The presence of a hepatitis virus infection was associated to drug addiction; indeed in 91 drug abusers HIV/HCV co-infection was present in 80% of cases and HIV infection alone in 7.7%, p<0.0001. On the other hand, the association between unsafe sexual activity, whether homosexual or heterosexual, and sexual activity with a steady anti-HIV positive partner with HCV infection was less evident, although the high prevalence of anti-HCV in these cases (10.4%, 15.4% and 26.4% respectively) clearly suggests that HIV infection may improve the sexual transmission of HCV. No substantial differences in the level of immunodeficiency, nor in the HIV viral load nor in the frequency of AIDS cases were observed between patients with HIV infection alone and those with HIV/HCV co-infection. In fact, the percentage of patients with AIDS was similar in these two groups. However, we observed a statistically significant association between an advanced HIV clinical stage and the presence of HIV/HCV co-infection (p<0.005), since subjects with co-infection more frequently than with HIV infection alone were in the CDC-B clinical stage. The presence of a more severe liver disease was linked to a multiple hepatitis virus infection, regardless of the degree of immunodeficiency.