Seroepidemiologic studies show that Kaposi's sarcoma herpesvirus (KSHV) is more prevalent in those populations at higher risk to develop Kaposi's sarcoma (KS). Anti-KSHV antibody titer is also higher in those who develop KS. KSHV is a sexually transmitted disease among homosexual men, but other routes of transmission appear to be more important in Africa and Mediterranean Europe. KSHV encodes numerous cellular homologues that might be involved in KS and lymphoma pathogenesis. The characterization of these homologues provides insight into the functions of their cellular counterparts. KSHV is also unique among human herpesviruses by encoding chemokine homologues. Unlike cellular MIP1 alpha and RANTES, KSHV-chemokines are promiscuous in their receptor usage and do induce angiogenesis. They may also play a role in preventing central nervous system diseases in HIV-positive individuals.