Nine cases of giant unclippable aneurysms treated with the detachable balloon technique are reported. Adjunctive surgical bypass procedures and arterial ligation were also carried out in four and one cases, respectively. All the patients tolerated occlusion of the carotid artery (eight cases) or of both vertebral arteries (one case). Three patients developed neurologic complications: two transient and one permanent (blindness in one eye). The complications occurred when attempts were made to occlude the aneurysm lumen only to preserve the carotid blood flow. Permanent occlusion of the carotid artery appears safer than aneurysm obliteration. Surgical procedures are necessary if the patient does not tolerate permanent occlusion of the artery or if occlusion of the artery is insufficient to obtain thrombosis of the aneurysm.