29 out of 34 consecutive patients of pediatric age, operated upon for posterior fossa medulloblastoma, were divided into 2 groups according to the chemotherapeutic treatment (mtrathecal methotrexate or intravenous cyclophosphamide) received at random after surgery and radiation treatment. The modalities of irradiation and chemotherapy are described. 9 patients have not yet shown a local recurrence and are alive at various intervals after surgery. Only 1 patient with local recurrence is still alive 31 months after the primary operation. The mean actuarial survival of the whole series of patients is about 38 months. Differences between the two groups, concerning either the survival rate till local recurrence, or the general and neurologic conditions of survival, are not statistically significant. Hematologic toxicity was more pronounced in the group treated with cyclophosphamide, whereas late neurologic sequelae were a more prominent feature of the in-trathecal methotrexate trial.