The study of AIDS and cancer has resulted in an important convergence of clinical-epidemiological investigations, molecular research and virological studies. This shared effort has led to significant discoveries in the field of human carcinogenesis. In a relatively short time, several topics have been clarified, namely: (1) the spectrum of AIDS-related tumours has been identified; (2) the role of HIV in lymphomagenesis and in the development of Kaposi's sarcoma (KS) has been defined; (3) AIDS-related cancers have allowed the discovery and extensive biological characterisation of the novel virus human herpes virus 8 (HHV8), also called KS-associated herpesvirus; and (4) genetic, molecular, and phenotypic studies of AIDS-related lymphomas have contributed to the formulation of a pathogenetic and histogenetic model of B-cell non-Hodgkin's lymphomas (NHL).