The aim of this study was to evaluate the incidence and the management of hydrocephalus following ruptured intracranial aneurysms. The authors analyzed 223 patients with aneurysmal subarachnoid hemorrhage(SAH) during the last two years retrospectively. The results are summarized as follows. Eighty patients(35.9%) showed ventricular dilatation on a brain CT scan. Twenty-five patients(11.2%) required shunt surgery. Hydrocephalus was closely related to the amount of hemorrhage and the location of the ruptured aneurysm. Two of 9 patients with acute hydrocephalus, who were managed by extraventricular drainage(EVD) before definite aneurysm surgery. The shunt surgery was done before aneurysm surgery in 16 patients and rebleeding occurred in 3 patients. Radioactive isotope(RI) cisternography diagnosed communicating hydrocephalus in 11 patients and the lumboperitoneal shunt was performed in those cases. It is concluded that hydrocephalus following aneurysmal SAH is the communicating type, an indication for shunt surgery could be determined by RI cisternography, and lumboperitoneal shunting seems to be the best treatment of choice to avoid rapid decompression of the ventricles and to protect the already compromised cerebral hemisphere. Decompression of the ventricles before aneurysmal surgery should be avoided whenever possible.