The radiosensitivity of 9 cerebellar medulloblastomas (6 cases of preoperative irradiation, 2 cases of postoperative irradiation, 1 case of non-operation) was evaluated by serial computerized tomography (CT). Six patients were males and 3 were females, and their ages ranged from 2 weeks to 18 years. A reduction ratio of 45 to 90% of the enhanced lesion was observed after irradiation with a total dose of about 20 Gy in 8 cases, excluding 1 case which was histologically diagnosed as “medulloblastoma with marked astrocytic differentiation.” The enhanced lesion had completely disappeared by the completion of initial radiotherapy in 2 cases and within 1 year in 4 cases (average: 6.6±3.1 months). In 1 case, the enhanced lesion which did not disappear at the completion of initial radiotherapy of 56 Gy was reduced by the delayed effect of radiotherapy. The results show that most primary lesions of typical medulloblastoma might be radiocurable, and that irradiation might be useful in the differential diagnosis of cerebellar tumors in younger patients. The site of recurrence after the initial radiotherapy was studied in 5 cases experienced in CT era. In all 5 cases, the site of recurrence was leptomeningeal dissemination, and no recurrence was found in the primary region except in 1 case. Therefore, prevention or treatment of leptomeningeal dissemination is very important in the therapy schedule for medulloblastoma.