Background: Aortic root ectasia might induce hemostatic disorders in patients with Marfan syndrome (MFS) via altered blood flow and rheology. The aim of this study was to explore the hemostasis in patients with MFS compared with healthy controls.Methods: In this cross-sectional case-control study we included patients with verified MFS (n=51) and sexand age-matched healthy controls (n=50). Main criteria were the aortic root in echocardiography and cardiac magnetic resonance imaging (MRI), and the coagulation status.Results: When compared with healthy controls, patients with MFS showed significantly increased diameters of the aortic roots (43.0±7.72 vs. 28.8±3.74 mm, P<0.001) and aortic Z-scores (4.36±2.77 vs. 0.948±1.09, P<0.001), considerably higher values of Multiplate ® tests (e.g., MP-ADP: 878.4±201.7 vs.