Acute leukemia is the major cancer of childhood, occurring in two forms: acute lymphoblastic leukemia (ALL) and acute nonlymphoblastic leukemia(ANLL), the latter being a composite of several varieties of acute leukemia. With optimum treatment today, successful remission occurs in a majority of children with leukemia, and significant numbers of these children are becoming long-term, disease-free survivors. These new successes have raised several new issues. Although progress has been slower in ANLL than in ALL, recent developments in acute leukemia investigations include new clues about the etiology and biology of the disease, more refined methods of classifying and subclassifying leukemia types, identification of prognostic factors that can be used to design treatment regimens, development and trial of new therapy plans for patients with a poor prognosis, and improvements in supportive care. For many children it is now more appropriate to consider leukemia a chronic life-threatening illness, and efforts are underway to reduce or prevent longterm medical and psychosocial complications so that today's cured children do not become tomorrow's disabled adults. For other children, leukemia remains a fatal disease, and attention is being directed toward improved understanding of the determinants of the disease and the development of innovative treatment strategies. If current challenges can be overcome, leukemia may be almost entirely curable within the next 20 years, and it may ultimately be preventable