In 44 consecutive cases of ruptured cerebral aneurysm, vasospasm was demonstrated pre- or postoperatively. These cases were examined by bilateral carotid angiography and computerized tomography (CT), and the relationship between the angiographically visualized distribution of vasospasm, the neurological symptoms, and infarction seen on CT was evaluated. Vasospasm occurred in only some intracranial portions of the cerbral arteries that were immersed in blood-stained cerebrospinal fluid. Angiographically, diffuse vasospasm extensively involving bilateral carotid systems indicated the gravest prognosis for patients. Vasospasm affecting one carotid system and the anterior cerebral arteries on the opposite side often produced permanent neurological deficits. On the contrary, when vasospasm was restricted to one carotid system or to bilateral anterior cerebral arteries, it was usually associated with temporary neurological symptoms; however, it always produced residual neurological symptoms if it extended to the ascending branches (M3) of the middle cerebral arteries. Computerized tomography definitely demonstrated a low-density area or infarction in the territory of the spastic arteries in 25 (71%) of 35 cases with vasospasm. A low-density area was always detected when vasospasm occurred in M3 segments.