OBJECTIVE: The safety and effectiveness of Guglielmi Detachable Coil(GDC) embolization for cerebral aneurysm has been well documented. However, domestically there are few reports. The purpose of this study is to analyze procedural complications that occurred during endovascular coilling performed for cerebral aneurysms retrospectively. METHODS: From January 1996 to December 2003, a total of 453 patients (484 aneurysms) who had undergone GDC embolization for cerebral aneurysm were selected. The aneurysms were classified according to rupture history, location, dome and neck size. Procedural complications such as aneurysmal rupture, thrombosis and occlusion of patent vessels due to coil escape were noted. RESULTS: Procedural complications occurred 49 cases (10.1%). Among these, there were 27 of procedure-related aneurysmal rupture (5.6%), 14 of thrombosis (2.9%), 8 of occlusion of patent vessels due to coil escape (1.7%). Death or severe neurological deficit were seen in 18 cases of procedure-related rupture, 9 cases of thrombosis and 4 cases of coil escape. Procedure-related mortality and morbidity rates for endovascular coiling were calculated to be 2.9% and 3.6% respectively. CONCLUSION: The potential complications associated with shape, size and relationship to parent vessels of each specific cerebral aneurysm must be considered carefully before treatment. In order to reduce complications, proper equipment, knowledge on the hemodynamics and vascular anatomy, and operator's expertise are desired.