Infants and young children who have brain tumors have a poor rate of survival and high treatment associated morbidity. A trial of mechlorethamine, vincristine (oncovin), procarbazine, and prednisone (MOPP) was performed to test the hypothesis that replacing radiotherapy with chemotherapy would improve survival and decrease long term morbidity of infants who have brain tumors. Between 1976 and 1988, 17 consecutive children less than 36 months old when diagnosed with medulloblastoma or ependymoma were treated with MOPP chemotherapy as primary therapy following surgical excision or biopsy of the tumor. Radiotherapy was reserved for recurrent disease. Ten of 17 children have survived without evidence of disease: medulloblastoma eight of 12 with median survival time of 10.6 years (range, 6.2 to 15.2 yrs); and ependymoma, 2 of 5 (at 13.0 and 16.0 yrs). Four of the 10 children with medulloblastoma and ependymoma who relapsed are now disease free at 7.5, 11.7, 12.2 and 13.5 yrs post relapse after receiving salvage therapy with cisplatin (n = 1) or irradiation (n = 3). All relapses occurred within 26 months of diagnosis. Data on growth demonstrated height less than the 5th percentile in all children who received cranial irradiation compared to 25 to 95th percentile for nonirradiated children. Intellectual ability for the group who did not require radiation was within normal range (mean IQ 100.1) and stable across annual assessments. Those who required radiation had lower IOs which continued to decline over time (mean IQ 85 at mean age of 5.8 years, declining to 63 at 10 years). In young children with brain tumors, primary chemotherapy with MOPP, omitting radiotherapy, provides improved neurodevelopmental outcome and survival.