The immunodeficient state that evolves in persons infected with the human immunodeficiency virus (HIV) appears to increase their risk of certain types of cancer. Among these are primary lymphoma of the central nervous system, undifferentiated non-Hodgkin's lymphoma, squamous cell carcinoma, anorectal carcinoma, and cutaneous malignancies. These malignancies are similar in incidence to those seen in other immunodeficient patients. Lymphoma, in particular, is associated with a more aggressive disease state. In HIV-infected patients, the disease is usually diagnosed at a more advanced stage, frequently has extranodal involvement, and usually responds poorly to chemotherapy. Viruses, such as Epstein-Barr virus and papillomavirus, have been implicated in the pathogenesis of lymphoma and other malignancies in immunosuppressed patients, including those with HIV infection.