Background: The enlargement of proximal aorta has been recognized to occur more frequently in patients with hypertension. However, the exact mechanisms leading to dilatation are not fully understood. We investigated the relation between aortic stiffness and proximal aortic dilatation in the hypertensive patients.Methods: We prospectively enrolled 35 hypertensive patients and 45 control subjects. All patients discontinued medications for at least 1 week before the study. Arterial stiffness was assessed through aorto-femoral PWV using the fluid-filled system and foot-to-foot velocity method. Proximal aortic diameter was quantitatively measured by aortogram with 6 Fr right Judkins catheter at the aortic arch, just below the root of left subclavian artery. The ratio of proximal aortic diameter to right common femoral artery was calculated. Results: The PWV, mean BP, aortic diameter and ratio of aortic to femoral diameter were higher in the hypertensive patients than in control group (11.9짹6.2 vs 9.8짹3.3, 107.4짹14.1 vs 95.6짹12.1, 30.5짹7.0 vs 27.8짹4.8, 4.7짹1.7 vs 4.0짹1.0, p=0.04, 0.02, 0.03, 0.02, respectively). There was a significant correlation between PWV and aortic diameter in the hypertensive patients (r=0.484, p<0.001). By multivariate regression analysis, independently of age and height, PWV was positively correlated with proximal aortic diameter in the hypertensive patients (棺 Coefficients=0.506, p<0.014), but was not correlated with mean blood pressure and pulse pressure. There were no significant correlations in the control group. Conclusions: PWV was an independent determinant of proximal aortic dilatation in the hypertensive patients. This result suggests that an increased wall stiffness of the proximal aorta could play part in the aortic dilatation related to hypertension.