Aortic dissection with the entrance tear in the descending thoracic aorta. Analysis of 40 necropsy patients. Clinical and necropsy findings are described in 40 patients who had aortic dissection with the entrance tear in the descending thoracic aorta. Their ages at death ranged from 39 to 91 years (mean, 66 years); 24 (60%) were men and 16 (40%) were women. Systemic hypertension was present by history in 33 patients (83%) and the hearts were of increased weight in 78%. Of the 40 patients, 31 (78%) had no operative intervention, while 9 (22%) underwent operation for aortic dissection. Of the 31 patients without operative therapy, the diagnosis of aortic dissection was established in life in 9 patients (29%) and at necropsy in 22 (71%). The interval from aortic dissection to death was 30 days or less in 13 patients (42%); rupture of the false channel was the cause of death in 9 patients (69%), renal failure in 2 (15%), and the cause was unclear in 2 (15%). The interval from aortic dissection to death was more than 30 days in 18 (58%) of the 31 patients without operative therapy. The cause of death in these 18 patients was related to the dissection in 11 (61%) (rupture of the false channel in 5; renal failure from dissection in 3, and rupture of the false channel of a second acute dissection in 3), but in the other 7 patients (39%) death was unrelated to the dissection but a nonfatal complication, specifically stenosis of the true channel from compression by a thrombus-filled false channel, occurred in 4 of these 7 patients. Thus only 3 (10%) of the 31 patients without operative therapy had no complications of aortic dissection. All nine patients who underwent operation had had an aortic dissection within 30 days, and the operation was performed because of a major complication of the dissection. Four patients survived 8 to 84 months after the operation. Thus early operative intervention (before the appearance of complications) appears justified in patients with aortic dissection with the entrance tear in the descending thoracic aorta to prevent rupture of the false channel acutely or after initial healing; to prevent renal failure from compression of renal arteries by an aneurysmal false channel; to prevent true channel stenosis from compression by a thrombus-filled false channel; and possibly to prevent the recurrence of acute dissection. 