Communicating hydrocephalus is one of the secondary complications of the subarachnoid hemorrhage from ruptured intracranial aneurysms. Possible factors for hydrocephalus were analyzed retrospectively in 183 patients with surgically treated ruptured intracranial aneurysms. The site of aneurysms were anterior communicating artery (54 cases), posterior communicating artery (66 cases) and middle cerebral artery (63 cases). Of the 170 cases, except 13 cases who died in the acute stage, shunts were required in 66 cases (39%) because of hydrocephalus. The incidence of hydrocephalus was significantly higher in those patients who had one or more of the following factors: (1) advanced age, (2) the aneurysm was located near the midline, (3) higher preoperative clinical grades, (4) thick clots on CT, (5) delayed ischemic neurological deficits and (6) a decompressive craniectomy. Surgical results of patients with hydrocephalus were worse than those of patients without hydrocephalus.