Aortic stiffness in 78 patients with juvenile forms of ascending aortic dilation with Marfan's syndrome was compared with aortic stiffness in 17 patients without Marfan's syndrome. In the ascending aorta and aortic arch, aortic stiffness was similarly increased in the 2 groups. In the descending aorta, however, aortic stiffness was increased only in patients with Marfan's syndrome.