An intensive multimodal therapy was developed for the treatment of a subpopulation of children with acute lymphoblastic leukemia (ALL) who had a predicted event-free survival of less than 40% on previously reported therapeutic regimens (at high risk for early relapse). Induction with multiagent chemotherapy and radiotherapy to bulky disease-bearing areas (peripheral lymph nodes and mediastinum) was followed by consolidation, CNS prophylaxis, and cyclical remission maintenance therapy. Ninety-six (96%) of 100 previously untreated patients, 1 to 17 years of age, attained a complete remission. Seven patients received other maintenance therapy or a bone marrow transplant in remission. Sixty-six of the remaining 89 (74%) are in continuous complete remission at 22+ to 72+ months (median, 44+ months). Marrow relapse occurred in 15 (17%), CNS relapse in 5 (6%), and testicular relapse in one. Sixty-six of the 93 evaluable patients (71%) (including the induction failures) are event-free survivors. Two patients died of infection during the induction phase. No patient died during consolidation or maintenance without recurrent disease. The patients spent a median of 19, 0, and 0 days hospitalized during induction, consolidation, and maintenance, respectively. The most common complications were bacteremia and mucositis during induction and mucositis and fever during periods of neutropenia in consolidation. Maintenance was well tolerated. We conclude that the treatment protocol is intensive, but the inherent toxicities are manageable with adequate supportive care. The life table--projected event-free survival of 69% +/- 5% 48 months from diagnosis is encouraging.