Kaposi's Sarcoma (KS) was first described one century ago as a disease occurring in elderly men manifested as an indolent cutaneous form. After the onset of human immunodeficiency virus type I (HIV-1) infection, KS became epidemic which, in association with HIV, presented as an aggressive, systemic disease. Recently, the recognition that a novel human herpes virus-8 (HHV-8) was highly prevalent among KS patients provided strong evidence to indicate that HHV-8 was the etiology of KS. The pathogenesis of KS in AIDS patients is still controversial, but there is evidence suggesting that KS is a cytokine-mediated disease, and that increased levels of inflammatory cytokines in AIDS patients were responsible for the aggressive pattern of the disease seen in such patients. The recently developed serological assays for detection of HHV-8 antibodies have made possible a better understanding of the prevalence of HHV-8 in different populations, and this has allowed a deeper understanding of HHV-8 epidemiology.