In an open-label, multicenter trial involving 233 patients with Marfan syndrome randomly assigned to receive either losartan or no further treatment, losartan was associated with a significantly reduced rate of aortic root dilatation over approximately 3 years (0.77 ± 1.36 mm vs 1.35 ± 1.55 mm in controls; P = 0.014). No losartan-associated differences were observed for dilatation of the ascending aorta, aortic arch, or descending aorta in the overall study population. Aortic volume did not significantly differ between the two treatment groups, nor did rates of prophylactic aortic root surgery, distal aortic surgical intervention, type B aortic dissection, or cardiovascular death (the last of which occurred in no patients).