OBJECTIVES: Recently, it was reported that microsurgical fenestration of the lamina terminalis (LT) may reduce the incidence of shunt-dependent hydrocephalus in aneurysmal SAH. The authors investigated the efficacy of the LT opening on the incidence of shunt-dependent hydrocephalus especially in the ruptured anterior communicating artery (ACoA) aneurysms. METHODS: The data of 71 ruptured ACoA aneurysm patients who underwent aneurysmal clipping in acute stage were reviewed retrospectively. The patients were divided into two groups according to the use of intraoperative microsurgical opening of the LT. Group I (n=36) included the patients with microsurgical fenestration of LT during routine pterional approach, Group II (n=35) consisted of patients in whom microsurgical fenestration of LT was not feasible. The rate of shunt-dependent hydrocephalus was compared between two groups by logistic regression to control for confounding factor. RESULTS: Ventriculo-peritoneal shunts were performed after aneurysmal obliteration in 18 (25.4%) patients. Overall conversion rates from acute hydrocephalus on admission to chronic hydrocephalus in each group were 29.6% (Group I) and 58.8% (Group II), respectively. There was no significant correlation between the microsurgical fenestration and the rate of occurrence of shunt-dependent hydrocephalus (p>0.05). CONCLUSION: Although this study cannot provide a definitive answer, the microsurgical fenestration of LT can play a negative role for reducing the incidence of chronic hydrocephalus. Surgeons should carefully decide the concomitant use of LT fenestration during surgery for the ruptured ACoA aneurysms.