We describe the case of a homosexual man with asymptomatic infection with human immunodeficiency virus and hepatitis B virus who developed primary hepatic lymphoma. The lymphoma presented with rapid enlargement of the liver, and ultrasound examination revealed multiple hypoechoic lesions within the liver. Histological examination of the liver showed massive replacement by lymphomatous tissue, as well as changes of chronic active hepatitis B. Immunohistochemical stains for hepatitis B surface and core antigens were strongly positive in almost all hepatocytes, but not in tumor tissue. Whereas the occurrence of lymphoma probably is related to HIV infection, possible interactions between hepatitis B virus and HIV infection are discussed. Thus, the presence of mass lesions within the liver in a patient with HIV infection should raise the possibility of hepatic lymphoma even if there is no evidence of generalized lymphadenopathy.