A 19-year-old man was admitted to the hospital because of blurred vision, visual field defect, diplopia and hypesthesia of the left face. Neurological examination on admission revealed impairments of the II, III, IV, VI cranial nerves bilaterally and the first branch of the V nerve on the left. X-ray films of the skull showed a marked decalcification of the sella and upper portion of the clivus. Cerebral angiography demonstrated a moderately vascularized, large tumor in the sella-clival region. The tumor was supplied mainly by the branches of the right internal carotid artery, which was occluded at the cavernous portion. CT scans showed a large, oval mass located at the mid-portion of the anterior and middle fossa. Hounsfield number of the tumor was approximately 64.0, but several high density spots, probably due to destroyed bone fragments, were seen inside. The tumor was markedly enhanced with contrast medium. Three successive craniotomies were carried out through right fronto-temporal approaches, but total removal of the tumor was not achieved. Histological examination of surgical specimens disclosed that the tumor was consisted of abundant multinucleated giant cells and fewer spindle shaped stromal cells. Postoperative radiotherapy by telecobalt was tried and a total dose of 70Gy was delivered to the residual tumor. Effect of radiotherapy was remarkable and the size of the tumor on CT was markedly reduced to the extent of 10% of the pre-radiation tumor size. The patient was discharged in a good condition and there have been no signs of recurrence for 10 months so far. On the basis of our case and cases reported in the literature so far, the authors discussed clinical and radiological features, difficulty in surgical treatment and radiosensitivity of giant cell tumor of the sphenoid bone.