The results of a series of 500 consecutive patients who underwent aneurysmal surgery between 1969 and 1980 are reported. The incidence of significant symptomatic hydrocephalus secondary to spontaneous rupture of an intracranial aneurysm was 16.4%. Hydrocephalus was most frequent after rupture of aneurysms of the anterior communicating artery. Only one-third of the patients had more than one episode of subarachnoid hemorrhage before surgery. In 64% of the patients with preoperative hydrocephalus, there was angiographic evidence of spasm. In certain cases, the hydrocephalus must be treated before the offending aneurysm can be managed.