(1) Analysis of the death certificates of 553 patients recorded as having died from leukemia showed that 57 per cent of deaths occurred over the age of 50, that more than 60 per cent of all leukemias were acute, and that 46 per cent of acute leukemias occurred over the age of 50. (2) Investigation of a selected group of 97 patients over 50 dying from acute leukemia suggested that the clinical, hematologic and histologic features of the disease are distinctive and can be differentiated both from those of acute leukemia in younger patients, and from chronic leukemia.