RECENT therapeutic advances, both surgical and medical, have greatly improved the previously grave prognosis of patients with dissecting aneurysm of the aorta. Yet, proper therapy of this life-threatening disease currently remains a matter of some controversy. The development of extracorporeal circulation has made a definitive surgical approach possible,1,2 but reported results are variable and marked by fairly high mortality and morbidity.3 Poor surgical results in some centers have led to the espousement of a vigorous medical attack on dissecting aneurysm, using drugs which both lower the systemic blood pressure and protect the aorta from further dissection by diminishing the velocity of ventricular contraction.4,5 The purpose of this report is to review the experience at the Massachusetts General Hospital in 113 proven cases of dissecting thoracic aneurysm admitted since 1950. During the first half of this time interval, no therapy was employed, whereas in the second half both