The purpose of this study was to investigate whether large arteries in subjects with Ehlers-Danlos Syndrome Type IV (EDS IV) exhibit altered morphological and functional characteristics that might indicate the risk of complications. Subjects with EDS IV, an inherited disorder of type III collagen, have a significant lifetime risk of arterial rupture. Magnetic Resonance Imaging (MRI) of the aorta and carotid artery was used to measure diameter, wall thickness, pulse propagation velocity, and spin-spin relaxation time constant (T2) of the artery walls. These measurements were made and compared by a two-sided t-test in 17 subjects with EDS IV and in eight age and gender matched sibling controls. Additionally, Spearman correlation was computed between measurements and the average longevity of affected relatives. Comparing controls to 15 subjects with no known prior aortic complications, we found no differences in the diameters of the descending thoracic and abdominal aortas, but did find ascending aorta dilatation in two subjects (13%). We also found a trend in EDS IV subjects toward higher wall thicknesses after normalizing by body surface area for both the abdominal aorta (P = 0.05) and the common carotid artery (P = 0.07). Finally, we found a significant negative correlation (R = −0.82, P = 0.02) between age-adjusted pulse propagation velocity and familial longevity. In conclusion, preliminary evidence suggests that elevated pulse propagation velocity, which indicates reduced vessel distensibility, may be a risk factor for complications of EDS IV. Ascending aorta dilatation and increased vessel wall thickness were also found in subjects with EDS IV and represent potential risk factors for future study.