Aim To evaluate the endothelial function in young hypertensive patients with no evidence of plaque formation and other risk factors for arterial sclerosis. Methods 45 young hypertensive patients and 20 matched healthy subjects were included in this study. Two-dimensional ultrasonography was used to determine the diameter of the brachial artery during reactive hyperemia caused by endothelium-dependent dilatation and the diameter of the same artery after sublingual glyceryl trinitrate induced by endothelium-independent dilatation. Result Despite the similarity of 2 groups in age, blood lipids and blood glucose levels, the increased percentage of the brachial artery diameter was lower in patients group than in normal control (12.32%±4.94% versus 16.63%±5.87%,P<0.01) during reactive hyperemia. There was, however, no significant difference in response to glyceryl trinitrate between two groups (18.94%±6.50% versus 21.02%±6.65%, P>0.05). Conclusion Endothelial dysfunction is present in young patients with essential hypertension before clinical evidence of atherosclerosis.