We analyzed the management of 310 patients with acute subarachnoid hemorrhage from a ruptured intracranial aneurysm, 280 of whom survived to operation, according to preoperative neurologic function, location and size of the aneurysm and timing of operation. Severe initial bleeding, rebleeding (usually within two weeks) and delayed ischemia were major preoperative problems; 10 per cent died, and 13 per cent deteriorated before operation. Operative mortality was 5 per cent, ranging from 1.6 per cent of patients with normal preoperative neurologic function to 35 per cent of severely disabled patients. Intraoperative complications (5 per cent of cases) related chiefly to the size and location of the aneurysm, but postoperative delayed ischemia (minor and reversible in 10 per cent and severe in 5 per cent) related to timing of operation and occurred primarily in patients afflicted within the previous 10 days. The results of surgical treatment, including preoperative deaths, were better than the natural history of the illness, the difference being apparent after one month's observation.