Twenty years ago when Children's Cancer Association of Japan was born, the diagnosis of childhood leukemia amounted to a death sentence. Only 20% or so of children with leukemia survived more than 5 years. Since then, enormous improvements have been achieved regarding our understanding on the etiology, diagnosis, and the treatment of childhood leukemia. Now, 70% of children with leukemia survive and enter adult life. Even though the improved survival rate of children with leukemia represents a medical success story, we now face new problems. The first problem is the fact that we still lose 20-30% of patients with childhood leukemia. To address this problem, we need to understand the etiology, epidemiology, and biology of leukemia; to identify the patients at greater risk; and to develop adequate treatments. The second problem is the treatment itself. Even though efficacious, the modem treatment for leukemia is a grueling experience for children and their families. We should develop a total care system for families and children based on a deep understanding of their needs. The third problem is the aftereffects of the treatment and of cured leukemia. Extensive radiation and chemotherapy have an entirely different spectrum of long-term effects on children than on adults. These treatments in the early stage of life, when the mind and body are developing, create many physical and psychological problems. These are the present problems of childhood leukemia.