A 28 year-old-male sufferred left third nerve paresis. A pattern of complete and isolated paresis was observed. Neuroimaginings and conventional cerebral angiography revealed abnormally enlarged middle cerebral artery. Because of its fusiform nature, the abnormality was left untreated surgically. The third nerve palsy began to resolve within a week from onset after prednisolone administration. The present case was interesting because of resulting from fusiform dilatation of middle cerebral artery which was the only finding related to the third nevre palsy and early recovering of pupil.