Human herpesvirus 8 (HHV-8, KSHV) was discovered in 1994 by means of a molecular biology approach which permitted to characterize fragments of its genomic sequence. The partial analysis of nucleotide sequence showed that HHV-8 was closely related to herpesvirus saimiri and Epstein-Barr virus, two members of Gammaherpesvirinae sub-family. So far, the virus has been neither isolated nor observed using electron microscopy. It is only detected by means of polymerase chain reaction (PCR) and molecular hybridization. HHV-8 detection in human tissues is strongly associated with three diseases: Kaposi's sarcoma, body-cavity-based lymphomas and Castleman's disease. This association raises the question of the causative role of HHV-8 in the occurrence of these three disease.