Clinical bleeding tendency and tests of immune function were studied prospectively in 11 human immunodeficiency virus (HIV)-infected hemophiliacs with immune thrombocytopenic purpura (ITP) and a platelet count less than 50,000/microL. These 11 patients represented 13% of a well-characterized cohort of 87 HIV + hemophiliacs. ITP developed a mean 3.5 years after seroconversion, mean platelet count at presentation was 36,000/microL (range 15,000 to 49,000/microL), and the mean age at seroconversion was 37.1 years. Nine patients (82%) suffered bleeding complications, including four with intracranial hemorrhage, which was fatal in three. At the onset of ITP, five had AIDS and six were asymptomatic. Mean T4 lymphocyte count at onset of ITP was 126 +/- 32/microL (range 5 to 267/microL). Sustained treatment responses occurred with intravenous gammaglobulin (2 of 2), one of whom spontaneously remitted, and with zidovudine (1 of 2), but not with steroids (0 of 6) or danazol (0 of 3). In conclusion, 13% of a cohort of HIV + hemophiliacs has developed ITP with platelets less than 50,000/microL, a significant proportion of whom (82%) have experienced bleeding complications. It is recommended that treatment for ITP in HIV + hemophiliacs be instituted once the platelet count falls below 50,000/microL in order to avoid serious hemorrhagic sequelae.