The Japanese Health and Welfare Ministry approved Guglielmi detachable coils (GDCs) for clinical use in 1997. This approval makes it possible to compare GDC embolization with surgical clipping from the same standpoint. We review treatment of aneurysms in our hospital in 1997 and focus on the role of embolization in treating aneurysms. We always examined patients with cerebral aneurysms as a possible candidate for neurosurgical clipping. If the patient had any difficulties and/or problems on neurosurgical clipping (surgically difficult location, high age, poor grade, other cerebro-vascular disease, etc.), the patient was treated by intraaneurysmal GDC embolization. The site of the aneurysm was ICA in 23, MCA 6, AcomA 3, ACA 3, VA 2, BA 11, PCA 1.Eighteen patients with ruptured aneurysm were treated in the acute stage. In this period, another 90 patients with ruptured aneurysm were treated by surgical clipping in the acute stage. The Hunt and Kosnik grade was II in 4, III in 6, IV in 4, V in 4. Spinal drainage was set in 13 patients and tissue type plasminogen activator was administered via the drainage in 7. According to the Glasgow outcome scale, good recovery or moderate disability was obtained in 3 out of 4 Grade II patients, 6 of 6 Grade III, 2 of 4 Grade IV, and 1 of 4 Grade V. Three patients died of distal embolization (technical complication), acute myocardial infarction, and cerebral vasospasm. There were no patients with rebleeding after embolization. In the patients with unruptured aneurysm (23 patients with 27 aneurysms) or a ruptured aneurysm treated in the chronic stage (4 aneurysms), 13 aneurysms were treated by neck plasty technique. Two patients aggravated clinically by complication at discharge. Rupture of the aneurysm occurred in 1 patient who had a very complicated aneurysm, resulting in body filling.Complications with persistents neurological deficit were aneurysm perforation in 1, distal embolism in 2, and hemorrhagic tendency due to systemic heparinization in 1. In conclusion, intraaneurysmal GDC embolization is a useful and effective treatment, especially for aneurysms located on posterior circulation, high-aged patients, patients with poor grade, and patients with systemic disease. However, there remains some problems such as possibility of technical complications and no information for long-term stability.