• Aortic aneurysms, whether sacciform, fusiform, or dissecting, can now be corrected surgically by techniques here described. The diseased part is extirpated, and function is restored either by repairing the remaining part or by using homografts or suitable plastic substitutes. The results of 313 such operations are given. In 83 cases the aneurysms involved the thoracic aorta and in 230 the abdominal aorta. The hazards of the operation are greatest for aneurysms lying closest to the origin of the aorta and diminish as the distance from the heart increases. For operations on segments proximal to the origin of the left subclavian artery a temporary shunt must be used around the occluded segment; for operations distal to this point but proximal to the seventh thoracic vertebra hypothermia effectively prevents ischemic complications. Special precautions are necessary also in the abdominal aorta, where the possibility of causing fatal ischemic damage to important viscera by interrupting flow through the cel[ill]ac, superior mesenteric, and renal arteries must be avoided. With improvements in technique the operative mortality has been steadily reduced and complete relief of symptoms has usually been achieved. There has been a significant increase in the life expectancy of patients with a disease that until recently was progressively disabling and ultimately fatal.