This study examined the relations between age, arterial distensibility, and systemic hemodynamics in patients with the Marfan syndrome. The study group included 170 patients referred to a specialist clinic, of whom 55 (age 26 ± 12 years) were diagnosed as having Marfan syndrome. The remaining 115 patients (age 25 ± 14 years) formed a control group. Each patient underwent echocardiographic examination, with measurement of ascending aorta diameter at end-diastole and end-systole, and aortic flow velocities. The elastic properties of the aorta were indexed by calculation of aortic distensibility, wall stiffness, and systemic pulse wave velocity. Mean end-diastolic aortic diameter in the Marfan group (38 ± 9 mm) was greater than that in the controls (26 ± 4 mm, p < 0.01). Resting heart rate and aortic flow velocities were similar in the 2 groups, but systemic arterial pulse pressure was greater in the Marfan group (50 ± 12 mm Hg) than in the controls (41 ± 8 mm Hg, p < 0.01). Aortic diameter increased with age in both groups, but at all ages the Marfan group exhibited greater aortic diameters (p < 0.05). Aortic distensibility was less in the Marfan group (2.6 ± 1.3 cm2 · dynes-1. 10-6) than in the controls (6.2 ± 2.1 cm2 · dynes-1 · 10-6, p < 0.01), and the aortic wall stiffness index was greater in the Marfan group (7.9 ± 3.4) than in the controls (2.8 ± 0.6, p < 0.01). Aortic wall stiffness increased with age and aortic diameter, but at all ages the Marfan group exhibited a stiffer aorta for a given diameter than did the controls. Systemic pulse wave velocity was greater in the Marfan group (621 ± 139 cm · s-1) than in the controls (394 ± 62 cm · s-1, p < 0.01). In patients with the Marfan syndrome, the aorta exhibits markedly abnormal elastic properties from an early age, including increased stiffness and increased systemic pulse wave velocities.