Human herpesvirus 8 (HHV-8) is associated with all epidemiological forms of Kaposi's sarcoma (KS), multicentric Castleman's disease and primary effusion lymphomas. HHV-8 is a gamma herpesvirus and his genome consists of an estimated 140 kb long unique coding region. Sero-epidemiologic studies support the findings that infection by HHV-8 in the occidental countries is not ubiquitous. The main routes of transmission for HHV-8 is sexual contact at least in homo-sexual men, however distribution of the prevalence of HHV-8 in Africa suggests that this virus could be transmitted by other ways such as mother to child or child to child. Analysis of the genome of HHV-8 identified an imprecedent numbers of genes implicated in cellular growth which have potentially a major role in tumorogenesis. Morphologic studies based on electron-microscopy, immunohistochemistry and in situ hybridization suggest that most of the cells in HHV-8-related tumours are latently infected. Efforts must concentrate on finding the best systems for growing the virus in cell cultures and in the strategy of treatment and (or) prevention of HHV-8-related tumours especially in organ transplant patients.