Incarcerated persons have high rates of infectious diseases. Few data on the prevalence of sexually transmitted diseases in prisoners are available. This multi-center cross-sectional study enrolled 973 inmates from eight Italian prisons. Demographic and behavioral data were collected using an anonymous standardized questionnaire and antibodies to HIV, HCV, HBV, HSV-2, and HHV-8 were detected in a blood sample obtained from each person at the time of the enrollment in the study. Two hundred and two out of the 973 subjects (20.7%) had antibodies against HHV-8. HHV-8-seropositive subjects were more likely to be older than 30 years with a higher educational level. HHV-8 infection was associated significantly with HBV (P < 0.001) and HSV-2 (P = 0.004) seropositivity and with previous imprisonments. Multivariate analysis showed that HHV-8 infection in Italian inmates was associated with HBV (P < 0.001) and HSV-2 (P = 0.002) seropositivity otherwise among foreigners inmates HHV-8 was significantly associated with HBV infection (P = 0.05). One hundred and eighty-six (21.2%) prisoners had anti-HSV-2 antibodies. At multivariate analysis HSV-2-positivity was significantly associated with HIV (P < 0.001) and HHV-8 infections (P = 0.003), whereas it was inversely associated with HCV infection (0.004). A relatively high seroprevalence of HHV-8 and HSV-2 among Italian prison inmates was found. The association of HHV-8 and HSV-2 infections suggest sexual transmission of these viruses among Italian prison inmates.