DRAMATIC in onset and catastrophic in its consequences, dissecting aneurysm of the thoracic aorta is a common disease that poses difficult problems in management. The dismal outlook for patients with this lesion treated conservatively has led to a vigorous surgical attack on the problem; results have been encouraging although the many difficulties associated with surgical therapy are well known.1234567 During a one-year period 12 patients with such aneurysms have been treated at the Massachusetts General Hospital by resection of the diseased aorta and prosthetic graft replacement. Nine of these patients survive. It is the purpose of this report to review . . .