The aim of this study was to determine the rate of acute hydrocephalus in patients with aneurysmal subarachnoid haemorrhage (SAH) and evaluate its clinical prognosis and treatment options. We recruited 152 patients who had ruptured cerebral aneurysms between 2006 and 2010. Sequential CT scans were performed 24-72 hours after haemorrhage to examine the development of acute hydrocephalus following aneurysmal SAN. If hydrocephalus was present but the patient's condition was stable, the patient was closely monitored for 48 hours before undergoing a repeat CT scan to evaluate ventricular changes. To exclude aneurysm rebleeding, repeat CT scans were performed frequently in patients who continued to deteriorate clinically, and external ventricular drainage was performed if the deterioration was due to worsening hydrocephalus. In clinically stable patients with persistent hydrocephalus and patients with external ventricular drainage, lamina terminal's fenestration was performed during aneurysm clipping, and the procedure's therapeutic efficacy was evaluated at the postoperative follow-up. The overall incidence of acute hydrocephalus following aneurysmal SAH was 17.8% (27/152). Of these patients, 29.6% (eight of 27) recovered spontaneously within 48 hours of hydrocephalus development, 37.0% (10/27) required external ventricular drainage, and 33.3% (nine of 27) remained clinically stable with persistent hydrocephalus during the observational period. Hydrocephalus was significantly alleviated in eight of 11 patients who underwent lamina terminalis fenestration, and no related complications were observed during follow-up. Three patients, for whom intraoperative fenestration was ineffective, underwent shunt surgery. Our results showed approximately 30% of patients with acute hydrocephalus following aneurysmal SAN recover spontaneously. In the majority of patients with persistent hydrocephalus, lamina terminalis fenestration performed during aneurysm clipping is effective. Ventriculoperitoneal shunting can be considered in the remaining patients. (C) 2011 Elsevier Ltd. All rights reserved.