OBJECTIVE To compare plasma concentrations of biomarkers of endothelial dysfunction between patients with primary aldosteronism (PA) and essential hypertension (EH), and to determine whether elevated levels of these biomarkers could predict development of early organ damage. METHODS Thirty-six PA patients and 39 EH patients matched for age, sex, blood pressure and duration of hypertension were included in this study. Plasma levels of biomarkers reflecting endothelial dysfunction (von Willebrand factor, vWF; soluble intercellular adhesion molecule 1, sICAM-1; and oxidized low density lipoprotein, ox-LDL) were detected and compared between PA and EH patients. Left ventricular mass index (LVMI) determined by echocardiography, 24-hour urinary protein quantitative determination and urinary albumin excretion rate (UAER) were analyzed to evaluate early organ damage. Left ventricular hypertrophy was defined as LVMI > 125 g/m(2) in men and > 120 g/m(2) in women, and UAER between 20 µg/min and 200 µg/min was defined as microalbuminuria. RESULTS vWF [(122.3 ± 53.8)% vs. (113.1 ± 68.3)%], sICAM-1 [(401.0 ± 74.1) µg/L vs. (300.9 ± 87.0) µg/L], ox-LDL [(13.6 ± 10.0) U/L vs. (8.1 ± 5.9) U/L], LVMI [(124.7 ± 33.6) g/m(2) vs. (109.1 ± 25.7) g/m(2)], 24-hour urinary protein quantitation [24 h UPQ, (0.17 ± 0.10) g vs. (0.09 ± 0.04) g] and UAER [(25.9 ± 7.7) µg/min vs. (9.7 ± 5.9) µg/min] were significantly higher in PA group than in EH group (all P < 0.05). Elevated plasma vWF, sICAM-1 levels and plasma aldosterone concentration independently predicted microalbuminuria. Whereas, elevated plasma vWF and ox-LDL levels, plasma aldosterone concentration and systolic blood pressure independently predicted left ventricular hypertrophy. CONCLUSION Patients with PA have severer endothelial dysfunction reflected by multiple biomarkers and earlier organ damage than patients with EH, and plasma aldosterone concentration and multiple endothelial dysfunction biomarkers could independently predict early organ damage.