Ten postoperative patients with intraventricular and subarachnoid dissemination of supratentorial gliomas were evaluated with a follow-up CT scan. The tumors consisted of 9 malignant gliomas and 1 astrocytoma. In 5 of the 9 malignant gliomas, the ventricles were surgically opened. In 4 of these 5 patients, a regional linear enhancement of the ventricular wall was observed in the early postoperative period. These findings were the initial findings indicative of tumor dissemination in the CSF space; a postoperative CT follow-up should be done within a few weeks after the operation, especially when the ventricles were ruptured. Subarachnoid dissemination and/or ventricular implantation could also be observed in the follow-up CT of such low-grade gliomas as optic gliomas, and there was no marked difference in the CT findings between low-grade and malignant gliomas. Concomittant progressive ventricular dilatation in early postoperative period was noted in 8 of the 10 patients with serial CT studies. It was considered that hydrocephalus was the another indication for advancing subarachnoid dissemination.