The age adjusted mortality rate of aplastic anemia in Japan decreased sharply in the mid-1970s; before this time, it had increased only slightly. A report on the survival rate among a substantial number of patients with aplastic anemia showed that patients who sought medical care at the hospital after 1973 had a better survival rate than those who sought care before 1973; the extent of improvement in the survival rate was almost equal to the extent of decrease in the mortality rate. The supply of platelet concentrates was found to increase with the decrease in the age adjusted mortality rate. Although there were several factors that affected the mortality rate from aplastic anemia, the major recognizable factor seemed to be therapeutic improvement, mainly due to the platelet concentrates. Probably neither a decrease in the incidence nor factors related to the data processing of vital statistics played a major role.