To examine the long term results of endovascular treatment of cerebral aneurysms with the Guglielmi detachable coil (GDC) system, follow- up (F/U) angiography was performed at 6, 12 and 24 months after the procedure. We analyzed 45 cases, 49 procedures of GDC treated cerebral aneurysms from 1997.6. to 2000.5. Follow- up angiography was achieved at 6M 43/45 (96%), 12M 29/33 (87%) and 24M 22/25 (88%). Angiographical changes were found 23/43 (53%) of the cases at 6M F/U. There were angiographical improvements in 12 cases (CP: complete occlusion, NR: neck remnant, PA: partial occlusion, PA-CP; 8, NR-CP; 1, PA-NR; 3) and angiographical worsening in 11 cases (CP-NR; 5, CP-PA; 3, PA-PA; 3) at 6M F/U. Two cases had been demonstrating progressive angiographical worsening at 6M and 12M F/U (CP-NR-PA). No angiographical change was found at 24M F/U. There was no case of hemorrhage or re-hemorrhage after GDC treatment. In cases of side-wall aneurysm, tight packing of the inflow side of the aneurysm and small neck aneurysm were thought to be causes of the angiographical improvements. In patients with wide neck aneurysms with partial occlusion result were angiographic worsening at the F/U. Other factors of angiographical worsening were improper working angle at the procedure and improper follow-up angle at the angiography and the intraluminal clot in the case of ruptured aneurysm.