The purpose of this study was to evaluate the effect of blood pressure (BP) rhythm on aortic functions in patients with metabolic syndrome. Seventy patients with newly diagnosed hypertension who fulfilled the metabolic syndrome criteria according to the Third Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (NCEP/ATP-III) were evaluated with 24-hour BP holter monitoring. According to BP rhythm, 35 patients with dipper BP pattern and 35 patients with non-dipper BP pattern were enrolled as two groups in our study. Systolic and diastolic diameters of the ascending aorta were measured by M-mode echocardiography and aortic functions (aortic strain, distensibility, and stiffness index) were calculated. The nocturnal systolic and diastolic BPs were significantly higher in non-dipper patients than the dipper group. According to clinical parameters including age, gender, height, weight, body mass index, waist circumference, clinical systolic, and diastolic BPs, we did not find significantly difference between the two groups. Aortic strain was significantly higher (6.63 +/- 3.37 vs. 1.81 +/- 0.92; P < .0001) and aortic distensibility was lower (2.38 +/- 1.18 cm(-2)/dyn/10(-6) and 6.66 +/- 3.67 cm(-2)/dyn/10(-6); P < .001) in non-dipper group. These findings suggest that aortic functions were prominently deteriorated in non-dipper hypertensive patients than dippers with metabolic syndrome.