The incidence of aplastic anemia among hospitalized adult patients was prospectively determined in this first study in Turkey, New cases of aplastic anemia among patients 14 years and older who were admitted to the study centers were included in a 3 year survey. Seventy-three patients fulfilled the diagnostic criteria, yielding a mean annual incidence rate of 1.14 cases in 10(3) admissions. The male-to-female ratio of the cases (1.6:1) differed from the almost equal ratio of the larger population of Turkey, The median age was 30 years and females were younger at diagnosis. The age distribution of the cases was different from that of the population; showing two incidence peaks in both sexes, The majority of the patients (89%) had severe disease. (C) 1997 Elsevier Science Ltd. All rights reserved.