The case of an 11-year-old boy is reported in whom two intramedullary lesions developed at the thoracic-cervical and thoracic-lumbar junctions 2 1/2 years after resection and irradiation of a medulloblastoma in the posterior fossa. There was no evidence of subarachnoid spread of the tumor. Magnetic resonance imaging was used to localize these lesions, and provided much better diagnostic information than either computerized tomography scans or myelograms.