The authors report on a series of 57 medulloblastomas in children operated upon -etween 1964 and 1976. Among these children, 44 completed the treatment with radiotherapy to the whole central nervous system. The postoperative mortality rate in 10.5%. Postoperative deaths occurred mainly in infants or when a tumour involved the brain stem. The five-year survival rate is 54% in the whole series. It rose to 71% in the patients who completed the treatment with radiotherapy. The study shows that the life of survivals is frequently impaired by mental or behavioural disturbances. IQ varies from 70 to 90 in 58% of the children; it is below 70 in 31%. Behavioural disturbances are found in 93% of cases. 82% have defective spatial orientation, dysphasia, or dysgraphia. In order to evaluate the responsibility of X-ray therapy for the development of these sequelae, the results have been compared to those of a series of cerebellar astrocytomas surgically removed, but not irradiated. The comparison shows that radiotherapy is at least partially responsible for the mental and behavioural disturbances. No relation was found between these disturbances and a persistent ventricular dilatation or an endocrine dysfunction. However the endocrine assessment showed growth hromone deficiency in 65% of the children, short stature in 55%, and compensated hypothyroidism in 58%.