From 1957 to 1984 direct and indirect isthmoplasty as described by Vossschulte has been the method of choice for surgical therapy of coarctation of the aorta in our hospital. A total of 317 patients have been so treated, 54 of whom were less than 12 months old at operation. The hospital mortality in this group was 15% and the mortality in patients older than 1 year was 3%. The early results were encouraging, but during follow-up an increasing number of postoperative aneurysms have been detected. During reinvestigation an aneurysm was diagnosed in 18 cases. Therefore, we have studied the cause of these aneurysms. To this point reoperation has been performed in 15 patients having late aneurysms. Extensive resection of a fibrous membrane of the aortic isthmus at the first intervention seems to be an essential predisposing factor for development of aneurysms. Microscopic examination of the aneurysmal wall revealed degeneration of the media in more than half of the patients. From our experience we conclude that the posterior fibrous ridge should no longer be excised and the Vossschulte operative technique should be viewed more critically.