Background: Medulloblastoma accounts for 15 to 25% of the intracranial malignancy and 24 to 40% of posterior fossa tumor of childhood. As its treatment, radiotherapy after operation has been performed. But in childhood, there was some difficulties in doing radiotherapy and in poor prognosis group, the 5 year survival rate was 30 to 60%. After the adjuvant chemotherappy was added, the 5 year survival rate increased to 60 to 80%. Since pre-irradiation chemotherapy has been done, the 5 year survival rate further increased recently. Thus we performed this study in order to evaluate the therapeutic effect of pre-irradiation chemotherapy. Methods : We observed 27 patients with medulloblastoma that its stage was more than T3a from January 1989 to December 1994 at Yonsei University Severance Hospital. Five patients was treated with radiotherapy after operation, 7 with radiotherapy and adjutant chemotherapy and 15 with pre-irradiation chemotherapy(adjuvant chemotherapy was done before and after radiotherapy). Adjuvant chemotherapy group was treated with vincristine, CDDP, ACNU and prednisolone. Pre-irradiation chemotherapy group was treated with vincristine(or VP-16) , CDDP and prednisolone before radiotherapy and after 2 weeks rest, adjuvant chemotherapy was done. Results: The 2 years survival rate was 60% for radiotherapy group, 70% for adjuvant chemotherapy group and 93% for pre-irradiation chemotherapy group by life table methods. Conclusion: In advanced medulloblastoma much better survival rate was noted in pre-irradiation chemotherapy group compared with radiotherapy group and adjuvant chemotherapy group. However further long term follow up will be necessary to evaluate the therapeutic effect of pre-irradiation chemotherapy in larger patient population.