We assessed the long-term follow-up results of platinum coil embolization and aneurysmography (ARG) with endovascular surgery for giant aneurysms. 24 cases of giant aneurysms were treated over a period of seven years. In the present study, the 16 of these for which surgical clipping was impossible so that only endovascular surgery was employed were investigated in detail. In 10 cases the cavernous sinus area was involved, in two each the tip of the basilar artery, and the bifurcation of the ophthalmic artery, and in one each the extracranial internal carotid and the vertebral artery. Since conventional angiography did not allow the position and size of the neck of 10 cavernous sinus aneurysms to be identified, making treatment decisions difficult, we applied the ARG developed by the senior author. Prior to treatment, balloon test occlusion of the parent arteries was performed. In all 10 cavernous sinus cases, ARG successfully revealed the morphology of the aneurysm. A small neck was diagnosed for seven of the aneurysms of the cavernous sinus and all those located at the basilar and ophthalmic arteries, making a total of 11, and for these endosaccular embolization was carried out. In the other 5 cases, proximal occlusion using Gold valve balloons was performed. Under ARG, embolization of the aneurysms could be safely accomplished with platinum coils, without dislocation of the coils into the parent arteries in all cases. In four out of 10 cases, re-opening of the aneurysms occurred after 2 months or longer, so that re-embolization was required. Regarding complications, transient monoparesis of the upper extremity was encountered in one case. After angiographic and MRA follow-up of 1-36 months (average, 13.8 months), 4 of 10 cases demonstrated complete occlusion, and 5 displayed an 80-90% reduction in blood flow. In only one case, involving a basilar tip aneurysm, was the treatment unsuccessful in preventing eventual rupture and death. In cases where the morphology of the aneurysm is unclear, ARG can be considered indispensable for determining the treatment modality and safe performance of localized embolization of the neck by endovascular surgery. However, since coils used for embolization of giant aneurysms may move or become compacted, re-opening can occur so that applications may be limited, especially with terminal type lesions with intraluminal thrombus, and the necessity for long-term follow-up must be emphasized.