The prevalence of anti-human herpesvirus 8 (HHV-8) antibodies was retrospectively assessed in a cohort of 248 consecutive HIV-1-positive patients followed up in an academic unit in Greece during a 14-year period and in 46 highly exposed, persistently HIV-seronegative (HEPS) individuals. The impact of the initial anti-HHV-8 status on tumorgenesis and mortality was studied. The first available serum sample from the department's pool was tested. Demographics and data regarding history of sexually transmitted diseases, Hepatitis B surface antigen (HbsAg) and hepatitis C (HCV) status were collected. Patients who developed either HHV-8-related or non-HHV-8-related neoplasms during long-term follow-up were also identified. Forty-eight percent of the HIV-1-positive patients and 56% of the HEPS subjects were found anti-HHV-8-positive. No difference was observed regarding the development of HHV-8-related or non-HHV-8-related neoplasia and mortality on grounds of initial anti- HHV-8 status. Mortality was positively associated with the presence of HBsAg. HCV infection showed a trend to be more common in anti-HHV-8-positive patients. In summary, the seroprevalence of HHV-8 among HIV-1-positive patients is higher than the one reported in the Western world. The initial anti-HHV-8 status is not a prognostic factor in HIV-1-positive individuals. The high seroprevalence in HEPS individuals possibly reflects their risk-prone lifestyle. HbsAg-positive status is a long-term negative prognostic factor in HIV infection.