CT scans were used to evaluate the development of the hydrocephalus, periventricular hypodensity (PVH) and the degree of the brain damage on 33 patients with the normal pressure hydrocephalus (NPH), following the subarachnoid hemorrhage (SAH), and the following conclusion can be drawn from our study. 1) NPH occurs in 33 cases out of 156 cases of subarachnoid hemorrhage (21%), and there was a relatively high incidence of normal pressure hydrocephalus following rupture of the anterior communicating artery aneurysm. 2) Factors causing NPH may be the arterial vasospasms and subarachnoid blood clot of the basal cistern verified by CT. 3) According to the repeated CT and lumbar tap after SAH, PVH, and, hydrocephalus usually become apparent around 7-10 days and most prominent around 3-4 weeks after SAH except for acute hydrocephalus appeared immediately after severe SAH. 4) The results were compared with CT findings and clinical response to shunting. The clinical improvements were achieved in cases (85%), in which CT showed PVH, small brain damage in the frontal lobe due to vasospasms or intracerebral hematoma, and no cortical atrophy. 5) Repeated CT can give better informations on the development of hydrocephalus in cases of SAH and can provide the indication for a shunt.