To investigate the relationship between endothelial function and carotid artery wall thickening in patients with early mild essential hypertension, the percent dilatation of humerus diameter and intimal-medial thickening (IMT) of common carotid artery was measured by using high-resolution ultrasound in 20 patients with early mild essential hypertension and 18 patients with normotension. The patients with hypertension had not been treated and their history of increased blood pressure was less than 12 months. In essential hypertension group, the percent dilatation of humerus diameter decreased significantly (2. 65 ±0. 98 % vs 6. 38 ±1. 61 %); IMT of carotid artery increased (0. 88 ±0. 16mm vs 0. 58± 0. 08). There was significant negative correlation between IMT and the percent dilatation of humerus diameter (γ= −0. 82,P<0. 05), and no correlation between IMT and 24 h mean systolic, diastolic pressure (γ= 0. 12 and γ= 0. 07, respectively;P>0. 05). Our results suggested that there was endothelial dysfunction in early mild essential hypertension. Endothelial dysfunction may not only contribute to the pathogenesis of hypertension but also serve as the most important inducing factor leading transformation from hypertension to atherosclerosis.