A patient with a giant aneurysm of the top of the basilar artery presented with severe progressive symptoms of brain-stem compression. There was inadequate collateral circulation to the upper basilar system. She underwent exploration of the aneurysm and, after it was found to be impossible to clip, a tourniquet was placed on the basilar artery for future occlusion with the patient awake. A saphenous vein graft was interposed between the left external carotid and the left posterior cerebral arteries. The previously unruptured aneurysm bled fatally 36 hours after surgery, just before intended occlusion of the basilar artery.