Clinically significant spinal implants develop in intracranial ependymomas. Spinal subarachnoid implants developed in 11 of 32 patients who received local irradiation at the University of Michigan between 1955 and 1972 for intracranial ependymoma. Seven of these patients received spinal axis irradiation for neurological disturbances resulting from the implants, and implants were found in the other 4 patients postmortem. Ten patients had infratentorial tumors, and one had a supratentorial tumor; nine tumors were poorly differentiated, two were well differentiated. The authors conclude that spinal irradiation is required if the tumor is poorly differentiated, or located in the infratentorial fossa.