Giant serpentine aneurysms are fusiform partially thrombosed aneurysms with a separate outflow tract to normal distal cerebral vessels. Three patients with giant serpentine aneurysms of the anterior and middle cerebral arteries were treated with endovascular occlusion of the aneurysmal lumen with coils or glue after balloon test occlusion of the involved vessel. In all 3 patients, leptomeningeal collateral circulation was sufficient to prevent distal ischemia.