To reduce the sequelae from CNS irradiation (RT), 16 children younger than 3 years with medulloblastoma-PNET (13 cases) and ependymoma (3 cases) were treated between 1987-1993 according to different postsurgical chemotherapy (CT) programs. None of these patients presented with metastases. Eleven patients were rendered disease-free by surgery, while 5 had residual tumor. Adjuvant therapy depended on patients' age, postsurgical status and parents' consent to radiotherapy (RT). Nine of the 16 infants remained alive in continuous complete remission from the first neoplasm (median follow-up 7 years). Three of them had been treated with CT alone and 6 with combined CT + RT (posterior fossa 4, whole CNS 2). Seven patients relapsed a median of 13 months after diagnosis, and all 7 of them died of their disease. Despite the omission of RT in 6 of the 16 patients and administration of only focal RT in 8 of the 16, the outcome of this series was satisfactory. Local failure (in 5/7 patients) was the major problem, despite the high dose of RT used in 2 of these 5. In 4 of 6 evaluable children school performance was satisfactory. One child in whom the entire CNS was irradiated developed glioblastoma multiforme 120 months after the first diagnosis of medulloblastoma.