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. The second problem is the treatment itself. Even though efficacious, the modem treatment for leukemia is a grueling experience for children and their families. 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.