Immunologic abnormalities resembling those seen in patients with the acquired immunodeficiency syndrome (AIDS) are frequently observed in multitransfused but otherwise healthy individuals with hemophilia. To determine whether there was clinical or laboratory evidence to suggest an abnormality of immunoregulation in persons with hemophilia before the recognition of AIDS, we examined data collected by the Hemophilia Study Group from 1975 to 1979 on 1,551 patients with factor VIII deficiency. The prevalence of lymphocytopenia and thrombocytopenia in patients over 5 years of age on entry was found to be 9.3% (94/1,013) and 5.0% (26/518), respectively. These rates were significantly different from a normal population (P less than .00001 and less than .0003). No cases meeting the definition of AIDS were noted during the study. However, on follow-up in 1984 of a cohort of 79 patients with thrombocytopenia or lymphocytopenia on two or more occasions during the study, eight patients (10%) with AIDS-related abnormalities, including idiopathic thrombocytopenic purpura, non-Hodgkin's lymphoma, generalized lymphadenopathy, and oral moniliasis without obvious cause were identified. Of the 79 patients, liver disease accounted for five of the ten deaths (12.6% mortality) observed during a minimum follow-up of five years after detection of cytopenia. Only one death was attributed to bleeding in the absence of liver disease. We conclude that (a) the frequency of lymphocytopenia and thrombocytopenia was increased in multitransfused factor VIII-deficient hemophiliacs before the advent of AIDS, and (b) persistent lymphocytopenia and thrombocytopenia appear to be strongly associated with liver disease, which was the leading cause of death in a cohort of hemophiliacs followed five or more years.