This paper presents the long-term results of treatment for children with acute lymphoblastic leukemia (ALL) as conducted by the Pediatric Oncology Group (POG) from 1986 to 1994. The data are presented using standard NCI/Rome risk criteria. The overall event-free survival (EFS) at 5 and 10 years were 70.9% and 67.3% for children with B-precursor ALL, 51.0% and 50.2% for patients with T cell ALL, and 22.4% and 20.9% for infants with ALL. Concomitant biologic studies found that in B-precursor ALL a DNA index (DI) of > or =1.16 and trisomies of both chromosomes 4 and 10 were good prognostic indicators for patients with B-precursor ALL. The traditional prognostic indicators (age and white count), DI and trisomies did not predict outcome in patients with T cell disease. Infants continued to do poorly overall despite more intensive therapy with rotating pairs of chemotherapy. We recommend continued reporting of study results using common risk criteria in order to facilitate comparisons both within and across study groups.