The characteristics and prognosis of patients with cystic medial necrosis of the aorta were reviewed. Subjects were 46 patients who underwent aortic and/or aortic valve surgery between August 1965 and October 1994. All had histologically documented cystic medial necrosis including 22 Marfan patients. The patients with Marfan syndrome were substantially younger (median age, 32 vs 50 years; p<0.05), and experienced annulo-aortic ectasia more frequently (81%(17/22) vs 46%(11/24); p<0.05 than those without the syndrome. Sixty-eight percent (15/22) of the Marfan patients and 63% (15/24) of the non-Marfan patients experienced complications with aortic dissection, although not to a significant degree. The hospital mortality rate was 14% (3/22) in the Marfan group and 21% (5/24) in the non-Marfan group, which was also not significant. Of the 38 survivors, developments in the health of 37 were completely followed-up until October 1997. The cardiovascular event-free rate for Marfan patients at 10 years (28%) was lower than that for non-Marfan patients (68%, p=0.057), whereas the actuarial survival rates at 10 years were nearly equal (72% for the Marfan patients and 74% for the non-Marfan patients). Reoperation was the first cardiovascular event in 77% (10/13) of the Marfan patients and in 14% (1/7) of the non-Marfan patients (p<0.05). Cardiovascular event was the main cause of late death both for Marfan patients (80%; 4/5) and for non-Marfan patients (86%; 6/7). In conclusion, independent of the presence of Marfan syndrome, careful follow-up is necessary for patients with cystic medial necrosis of the aorta to eliminate serious late complications.