In an attempt to find safe and effective methods of treating giant intracranial aneurysms, we have developed a one-step construction of giant experimental aneurysms in dogs with a yield of 100% patency of the parent artery and the experimental aneurysm without intraaneurysmal thrombus. Giant aneurysms were produced in the right thrombus. Giant aneurysms were produced in the right common carotid artery of nine mongrel dogs. Key features concerning the procedure were: (1) proximal placement of the aneurysmal neck, (2) 1 cm length as the aneurysmal ostea, and (3) postoperative aspirin therapy. This one-step construction of giant experimental aneurysms in dogs should prove helpful in evaluating a wide variety of treatment modalities of giant aneurysms in the laboratory. It also may be of additional value in investigative studies relative to catheters, balloons, and other similar techniques.