A group of 44 homosexual patients with immune thrombocytopenia and serologic evidence of infection with the human immunodeficiency virus (HIV) was observed for a total of 844 person-months. The risk of developing the acquired immunodeficiency syndrome (AIDS), an actuarial incidence of 36.5% in 37 months, was no different than that reported for seropositive homosexual men from New York who are nonthrombocytopenic and asymptomatic. A statistical analysis comparing the hazard function with a constant-risk model showed that the hazard of developing AIDS was not constant but increased with duration of seropositivity.