OPN (osteopontin), a pro-inflammatory cytokine, has recently emerged as a key factor in both vascular remodelling and the development of atherosclerosis. However, the relationship between OPN and atherosclerosis in patients without symptomatic cardiovascular disease is not clear. Therefore we measured plasma OPN levels and evaluated the correlation between plasma OPN levels and atherosclerosis as target organ damage in patients with EHT (essential hypertension). Plasma OPN levels were measured in 76 patients with EHT using a solid-phase sandwich ELISA. IMT (intima-media thickness), and V(d) and V(s) (mean diastolic and systolic flow velocities respectively) were evaluated by carotid ultrasound. The V(d)/V(s) ratio, an index of peripheral arterial resistance, was also calculated. The patients were divided on the basis of median OPN levels into a high-OPN group and a low-OPN group. The mean IMT and aldosterone levels were higher (P=0.024 and 0.031 respectively) and V(d)/V(s) was lower (P=0.007) in the high-OPN group than in the low-OPN group. Plasma OPN levels were positively correlated with mean IMT (r=0.308, P=0.0068) and negatively with V(d)/V(s) (r=-0.293, P=0.010). Stepwise regression analysis revealed that OPN was an independent determinant of mean IMT (P=0.007) and V(d)/V(s) (P=0.009), and aldosterone was an independent determinant of OPN. These results suggest that OPN plays a role in the development of atherosclerosis and may be a potential clinical marker for the prediction of atherosclerosis in patients with EHT.