OBJECTIVE Arterial stiffness is one of the early lesions of the arteries in patients with cardiovascular risk factors. Pulse wave velocity (PWV) is one form of measurement of arterial stiffness. The renin-angiotensin system seems to be involved in the inflammatory mechanisms that take place at level of the vascular wall. The aim of this study is to investigate the effect of olmesartan (angiotensin II type 1 receptor antagonist) in the arterial stiffness, measuring the PWV. Another secondary objective is to determine the antihypertensive efficacy with ambulatory blood pressure monitoring (ABPM). METHODS Seventy-one patients with mild-to-moderate essential hypertension were consecutively included. Clinical blood pressure (CBP), ABPM and PWV, automatized measurement between the carotid and femoral arteries using the Complior device (Colson, Paris, France), were determined in a baseline and after 16 weeks of treatment with 10-40 mg of olmesartan. RESULTS Sixty-four patients completed the study. The mean (standard deviation) age was 48.31 (9.69) years and 44.9% were men. A significant reduction of the PWV was observed. The basal PWV was 10.50 (1.87) m/s and after treatment was 9.26 (1.84) m/s (p < 0.0001). We found only a positive correlation between the decline of PWV and diastolic blood pressure (BP). We could not find such correlation with systolic BP. The reduction degree was higher in the youngest patients where BP decrease was less evident. The BP decreased in a significant way (p < 0.0001) doing so in CBP and in the periods of 24 h, diurnal and nocturnal. CONCLUSIONS Olmesartan has shown effective to decrease the arterial stiffness, mainly in young patients. This effect seems to be independent of the decrease of the systolic BP. Olmesartan reduces effectively the BP during the 24 h.