GDC (Guglielmi detachable coil)-embolization for the treatment of brain aneurysms was first published by Guglielmi in 1991 and has become an integral part of the treatment strategy for cerebral aneurysms in many places around the world. Low morbidity and mortality rates are set against the limited possibilities of aneurysm neck occlusion, especially in large necked aneurysms. Depending on the architecture and on the kind of coil distribution, recanalization of the neck is more or less frequent. Nevertheless, rebleeding rates are low. In our series of 211 brain aneurysms from March 1992 to June 1994, 74 (35%) patients underwent GDC-embolization. 4 patients received combined treatment (GDC-embolization and subsequent surgery). Follow-up angiography was performed on 41 patients (55%) at periods of 6, 12, and 24 months (mean follow-up 8 months). To demonstrate the results in a graphic display, the aneurysms were grouped according to location and size. The analysis of the follow-up results shows the highest occlusion stability in aneurysms of the basilar tip, followed by aneurysms of the PICA origin, the basilar trunk and the PCA. Less stability was obtained in aneurysms of the PCom followed by MCA, Acom and aneurysms of the internal carotid (C1, ophthalmic). Aneurysms of the posterior circulation show generally better results than those located in the anterior circulation. This makes (in combination with the increased surgical difficulties of aneurysms in the posterior fossa) the GDC-treatment especially useful for posterior circulation aneurysms.