51 medulloblastomas under 12 years of age were treated from 1966 through 1977. 50 patients underwent craniotomy and 39 of them completed postoperative radiation therapy. Surgical mortality rate of primary posterior fossa craniotomy was 8%. One year survival rate was 71.4%, 3 years 45.6% and 5 years 34.5%. Extent of surgical resection was found to affect the survival, and a group of radical or visibly total resection showed higher postoperative survival. Female patients enjoyed longer survival. The patients under 12 months of age showed poor prognosis. Reexploration of the posterior fossa failed to prolong the survival by more than 3 months.