Between 1964 and 1982, 862 patients with acute leukemia who were collected from medical institutions throughout the country had a survival of 5 years or longer. Their remission has been achieved mainly with a combination therapy of vincristine and prednisone in childhood acute leukemia and daunomycin, cytosine arabinoside, 6-mercaptopurine, prednisone (DCMP) regimen in adult acute leukemia. Among 320 relapsed patients, 88 (38.8%) of 227 children had a primary relapse in the marrow, 85 in the central nervous system (CNS), 37 in the testis/ovary, and 13 in a combined site. The large majority of adult relapsed patients relapsed in the marrow. Ninety-three patients who experienced only one relapse had a much longer prolongation of survival, not yet reaching a median over 14 years after diagnosis, compared to those experiencing two or more relapses. Survival curves in five groups of patients divided by length of maintained remission were investigated by the life table method. In children as well as adults, survival duration in patients on 5 or more years maintained remission was significantly longer than that in the other maintained groups. With respect to relation between frequency of CNS relapse and type of CNS prophylaxis, there was no statistically significant difference between patients who received CNS prophylaxis and patients who did not. However, a better survival was observed in patients who received CNS prophylaxis with cranial radiation plus intrathecal methotrexate. Thus, long-term clinical follow-up might provide important information for the therapeutic strategy against acute leukemia.