HIV infection is known to increase the incidence of Kaposi's sarcoma and non-Hodgkin's lymphoma. Kaposi's sarcoma preferentially affects homosexual men and risk varies by geographic area, suggesting there is an environmental cofactor for Kaposi's sarcoma in addition to HIV. Despite intensive investigation, the responsible cofactor has not been conclusively identified. HIV-associated non-Hodgkin's lymphoma affects all HIV transmission groups, and non-Hodgkin's lymphoma risk increases with duration of HIV infection and age. Epstein-Barr virus has been implicated in the pathogenesis of this tumor, but the precise mechanisms have not been worked out. Cervical cancer and anal cancer have a less certain association with HIV infection and immunodeficiency, although epithelial dysplasia at these sites does seem to be HIV-related. Children with HIV infection are additionally affected by increased incidence of leiomyosarcoma and benign leiomyoma, whereas adults with HIV infection do not seem particularly susceptible to this tumor, perhaps because of hormonal or growth-promoting factors. Apart from these specific disease associations, HIV infection and related immunodeficiency do not result in a generalized tumor diathesis. Prevention and management of HIV-associated cancers are becoming increasingly important as the HIV epidemic continues to grow.