Background Improved outcome for children with medulloblastoma requires new treatment protocols which incorporate chemotherapeutic agents that are capable of eradicating minimal residual disease in the primary posterior fossa site and in the leptomeninges and whose toxicities are tolerable. Procedure We treated 25 children with nondisseminated medulloblastoma with complete or near complete surgical resection of the posterior fossa tumor, 3,600 cGy craniospinal irradiation (CSRT) and 5,400 cGy posterior fossa irradiation followed by adjuvant chemotherapy with carboplatin and vincristine. Results The estimated 3-year progression-free survival (PFS) was 0.73 (S.E. ± 0.09) compared with a 3-year PFS of 0.69 in historical controls treated with surgical resection and CSRT but without chemotherapy. Six relapses occurred outside the posterior fossa and one relapse occurred both in the posterior fossa and in the lateral ventricle. The major acute toxicities were myelosuppression, anorexia and neuropathy. Conclusions Our experience with this adjuvant chemotherapy regimen with carboplatin and vincristine, as used by us, does not encourage its adoption in future clinical trials. Med. Pediatr. Oncol. 29:563–567, 1997. © 1997 Wiley-Liss, Inc.