Among 50 patients with subarachnoid hemorrhage (SAH) from aneurysm, computed tomography (CT) demonstrated evidence of bleeding in 28. In 12 cases, the location and configuration of the high-density blood cast visualized by CT was characteristic and predicted the site of the ruptured aneurysm. CT was reliable in identifying infarction, edema, localized hematoma, hydrocephalus, or rebleeding in patients with SAH and neurologic abnormalities. In four cases, the plain and contrast CT suggested a large intracranial aneurysm. These findings did not permit definitive diagnosis or precise anatomic detail of angiographically defined aneurysms less than 2.0 cm in size.