The authors analysed 74 cases of ruptured aneurysms confirmed by CT, angiography and surgery during the period from September 1982 to August 1984 at Keimyung University Dongsan Hospital for the study of the relationship between the amount of subarachnoid hemorrhage(SAH) detected by CT and the preoperative clinical grade (Hunt & Hess), the later development of cerebral vasospasm, ischemic neurologic deficit(IND) and the postoperative prognosis. We also attempted to investigate the relationship between the low density in the hypothalamus and/or midbrain on CT and the preoperative clinical grade and the angiographic vasospasm. There was no definite difference in age and sex distribution according to the severity of SAH on CT except in predominantly female cases of severe SAH(CT grade III). 75% of the cases with the absence of SAH(CT grade I) were preoperatively clinical grade I or II. However, 76% of the severe SAH cases(CT grade III) showed preopertively clinical grade III, IV or V. In case with no angiographic vasospasm(Ag0), 70% were shown to be clinical grade I or II. But in cases of severe vasospasm seen by angiography(Ag3), 80% were clinical grade III or IV. 17% of the cases that showed an absence of angiographic vasospasm(Ar0) showed a low density in the hypothalamus and/or midbrain on CT as did 48% of the cases with mild angiographic vasospasm(Ag1), 75% with moderate angiographic vasospasm(Ag2) and 100% of the cases with severe angiographic vasospasm(Ag3). It was noticed on the CT in cases of clinical grade I and II, there was a 14% and 24% low density in the hypothalamus and/or midbrain respectively. But in the cases of clinical grade III and IV, it was noticed that there was a 65% and 100% low density in hypothalamus and/or midbrain respectively. Ischemic neurological deficit(IND) developed in 9% of the cases having an absence of SAH(CT grade I) on CT and in 48% of the cases of severe SAH(CT grade III) on CT during the care if the patients. 100% of the cases showed good postoperative results in patients who had an absence of or thin SAH(CT grade I or II) on CT and only 50% of the cases who had severe SAH(CT grade III) obtained good postoperative results. The authors found a correlation between the amount of SAH and the preoperative clinical grade, the development of angiographic cerebral vasospasm, IND and the postoperative prognosis. The low density in the hypothalamus and/or midbrain on CT also has a relationship with the preoperative clinical grade and the development of angiographic vasospsm. We suggest that the severity of SAH on CT and the low density in the hypothalamus and/or midbrain may be of great value in the prediction of cerebral vasospasm and treatment of aneurysmal patients.