From 1985 to 1996, 18 patients with Marfan's syndrome underwent the Bentall procedure at Mount Sinai Hospital. They are compared with 38 patients aged < 40 without Marfan's syndrome who also underwent composite valve-graft replacement of the ascending aorta. The mean age of the non-Marfan group was 33 while that of the Marfan group was 29. Nearly three-quarters of each group were male. Aortic dissection was present in 33% of the Marfan group but only in 18% of the other group. Seventy-eight percent of the Marfan patients and 89% of the non-Marfan patients had aortic regurgitation. Twenty-one percent of the patients in the control group nevertheless had gross aortic pathology suggestive of Marfan's syndrome and may have had variants of the syndrome; 26% of the non-Marfan group had a bicuspid aortic valve. A modification of the Bentall procedure with implantation of coronary artery buttons was performed in the majority of the patients in both groups. Three patients, all in the group with Marfan's syndrome, required a concomitant mitral valve procedure. There was one death in each group. Two non-Marfan patients required reoperation; neither had dissection. Four patients with Marfan's syndrome underwent reoperation for distal disease in the aorta; they comprised one third of the Marfan patients who had aortic dissection. Three late complications occurred in the group with Marfan's syndrome: progressive cardiomyopathy; myocardial infarction; and late tamponade. There were also two late sudden deaths in the group with Marfan's syndrome, which may have been the consequence of aortic rupture. No difference in immediate operative mortality following the Bentall procedure was noted between patients with and without Marfan's syndrome, but young patients without Marfan's syndrome seem to have better event-free and long-term survival. In patients with Marfan's syndrome, the presence of acute dissection makes reoperation more likely, and sudden death from rupture still occurs despite careful postoperative surveillance. A higher incidence of severe mitral valve disease was found among young patients with Marfan syndrome than in controls.