The authors report a case of acute epidural hematoma occurring after evacuation of chronic subdural hematoma with continuous closed system drainage. Laboratory data of the patient including bleeding time were within normal limits. The cause of the postoperative intracranial hematoma was the rapid surgical decompression of the initial lesion, and we considered that it could be prevented if chronic subdural hematoma was treated using closed system drainage and slow decompression. But acute epidural hematoma occurred after this operative procedure and it was accelerated by evacuation of the chronic subdural hematoma through the drain. An emergent craniotomy and removal of the hematoma was performed, so the patient was discharged from hospital with satisfactory neurological recovery. A careful check of the evacuated hematoma volume is very important, and CT scanning should be immediately performed if postoperative hematoma is suspected.