Subdural hygromas are easily treated by trephination and drainage. Therefore, most neurosurgeons do not consider subdural hygromas seriously. However, various complications including intracerebral hemorrhage may develop after rapid drainage of subdural hygroma although rare. Postoperative intracerebral hemorrhage presents with a rapid deterioration of consciousness and focal neurological deficits occurring immediately after drainage of the subdural hygroma. The authors present an unfortunate massive intracerebral hemorrhage and pneumocephalus following drainage of the bifrontal subdural hygroma. The patient subsequently died. To prevent this disastrous complication, close neurosurgical observation and gradual drainage under a closed system seem mandatory. Possible pathogenic mechanisms for this unfavorable complication is discussed with a review of pertinent literatures.