The authors report on an anti-hepatitis C virus antibody (HCV Ab) prevalence (6.9%) in 622 homo-bisexual males from Northern Italy, voluntarily attending an HIV and STDs screening program in the period 1984-89. The anti-HCV antibody prevalence shows a significant correlation with: i) presence of serological markers for HBV (O.R. = 3.12, 95% C.I. = 1.53-6.52) and HIV (O.R. = 12.09; C.I. = 6.52-22.52) infection; ii) a stable relationship with an anti-HCV antibody positive partner (O.R. = 7.79; 95% C.I. = 2.50-23.90); iii) more than twenty different male partners per year (O.R. = 2.55; 95% C.I. = 1.17-5.66). These data demonstrate the existence of a sexual transmission of HCV among homosexuals. This route might contribute in maintaining endemic levels of HCV infection in the homo-bisexual population and it might represent an important way of spreading the virus in the general population too.