Early return of reflected pressure waves increases the load on central arteries. In patients with Marfan syndrome (MFS), this may increase the risk of aortic rupture. To assess whether wave reflection is elevated in MFS, we measured central pressure and flow waveforms in 26 patients (age 13-54 yrs) and in 26 age and sex matched controls (CTRL) using ultrasound and magnetic resonance imaging. Aortic systolic and diastolic cross-sectional area was measured at 4 levels: ascending (AA) and descending (DA) aorta, diaphragm (DIA) and low abdominal aorta (AB). From these, local characteristic impedance (Z_0-xx) was calculated as well as local reflection coefficients (_xx-yy). Calculated global wave reflection indices were the augmentation index (AIx) and the ratio of backward-to-forward pressure wave (P_b/P_f). The aorta was wider in MFS at AA (P<0.01) and DA (P<0.01). Aortic pulse wave velocity (PWV) was 42 cm/s higher in patients (P<0.05). Z_0-xx was not different between groups, except at DA where it was lower in MFS. In CTRL, _AA-DA was 0.31±0.08, _DA-DIA was 0.00±0.11 while _DIA-AB was 0.31±0.16. Mean values of _xx-yy were not different between patients and controls. In CTRL, ageing diminished _AA-DA, while _DIA-AB increased with age. Clear age-related patterns were absent in MFS. AIx or P_b/P_f were not higher in MFS than in CTRL. Nevertheless, there were indications for enhanced wave reflection in young MFS patients. Our data demonstrated that the major determinants of AIx were PWV and the effective length of the arterial system and, to a lesser degree, heart rate and P_b/P_f.