From 1955 to 1965, 117 patients with idiopathic acquired hemolytic anemia were observed. Survival was 91% at one year, 76% at five years, and 73% at ten years. The data suggest that survival has no significant relationship to the age of the patient at the time of diagnosis, to sex, or to hemoglobin level, leukocyte count, platelet count, reticulocyte count, or presence or absence of splenomegaly or a positive Coombs' test at the time of the initial examination. Survival data suggested (but did not confirm) that, at the five- and ten-year periods of observation, patients treated with both splenectomy and corticosteroids have a more favorable prognosis than do patients treated with corticosteroids alone.