The logical treatment of aneurysms consists of excision and the restoration of the normal blood flow. Such a procedure requires temporary occlusion whenever lateral aneurysmorrhaphy is not feasible or vessel segments have to be replaced by homografts. Although the cross-clamping of many major vessels or even of the abdominal aorta is well tolerated, the temporary occlusion of the aorta at higher levels is dangerous because of anoxemia in the tissues distal to the obstruction. In view of the fact that the central nervous system is the most vulnerable part, it would seem preferable to maintain circulation in the common carotid arteries and thoracic aorta at all times during operation. Thus, the surgical management of aneurysms involving the aortic arch represents a specific problem and necessitates in certain cases a complete diversion of blood flow during the period of aortic obstruction, provided this can be done without great technical disadvantages.