We studied retrospectively the series of 24 patients (17 men, 7 women), median age 25.5 years (range: 16-57), operated upon for a cerebellar medulloblastoma from March 1979 to June 1988. The tumors were diagnosed for all the patients by C.T. scan and by M.R. imaging for the six last patients. Seven tumors (29.2%) were located in the fourth ventricle, 2 in the vermis (8.3%), 9 in the cerebellar hemisphere (37.5%), 5 in the vermis and cerebellar hemisphere (20.8%). One patient had a diffuse infiltration of the cerebellum. All patients have been operated on (complete removal: 15 patients (62.5%), subtotal removal: 8 patients (33.3%), biopsy: 1 patient). Operative mortality was 8.3% (2/24). One patient died at two months from septicemia. The twenty-one surviving patients received radiotherapy. Twelve patients received both radiotherapy and chemotherapy. Six patients (25%) died during the follow up at 17, 22, 24, 60, 84 and 85 months. One patient is lost to follow up at 45 months and 13 patients are living at the closing date (June 1989). For the total group (n = 24) the probability of survival at 5 years was 64.8% (C.I. 95%: 42.8%-86.8%). Among the 21 patients who received radiotherapy alone or radiotherapy and chemotherapy the probability of survival at 5 years was 74.4% (C.I. 95%: 52.2%-96.7%). We studied the following predictors of poor outcome: age, sex, prognosis subgroups as defined by Chang et Coll., extension of tumor removal, adjunction of chemotherapy, histology. None of these factors was statistically related to the survival duration.(ABSTRACT TRUNCATED AT 250 WORDS)