A new human virus belonging to the herpesvirinae family was recently isolated and characterized. This virus called human herpesvirus 8 is considered as the etiological agent or as a major cofactor of all the clinical forms (HIV associated or not) of Kaposi's sarcoma. HHV8 is also associated with rare B cell lymphomas called body cavity based lymphoma (BCBL) or Primary effusion lymphoma (PEL) occurring in the body cavities mainly in AIDS patients and of some cases of the multicentric form of Castleman's disease. Only preliminary data are available on the epidemiological characteristics (modes of transmission in endemic regions, geographical distribution ...) of the HHV8 infection but should rapidly beneficiate of the establishment of specific and reliable serological tests. Nevertheless, it appears that the HHV8 seroprevalence is very high (15 to 50%) in the adult general population of areas having a high incidence of Kaposi's sarcoma as some east african countries and at a lesser extend as some mediterranean areas as southern Italy or Greece. In the occidental world, the seroprevalence of HHV8 seems very low (0 to 5% in the blood donors) except in some populations at risk for sexually transmitted diseases especially in the homosexual male group. Preliminary data indicate the existence of a low genetic variability of HHV8 in several regions of its genome, with however the presence of molecular subtypes linked possibly to the geographical origin of the infected patients.