Convulsive seizures within 48 hours after intracranial operations using a craniotomy were reviewed. Incidence was 8.9% (44 of 493 operations): 13.5% of brain tumor operations and 3.8% of aneurysmal operations. We demonstrated that preoperative seizures, sites of lesion, sub-therapeutic anticonvulsant levels, and postoperative local organic lesions were important factors causing the immediate postoperative seizures. Among them, a survey of postoperative computed tomography scans disclosed nine intracerebral hemorrhages, eight cases of cerebral edema, and four cerebral infarctions in the 44 patients; such major complications had a significant correlation with postoperative seizures (p less than 0.005).