Background: In young ADPKD patients, we have previously found an impaired endothelium-dependent relaxation in small resistance vessels but a normal flow-mediated dilatation of the brachial artery. The present study investigated arterial stiffness in early ADPKD by pulse-wave analysis (PWA) and measurement of pulse-wave velocity (PWV). Methods: 18 young normotensive ADPKD patients with normal renal function and 18 controls were studied by applanation tonometry with the SphygmoCor® equipment. Parameters included an estimate of aortic blood pressure, augmentation index (AIx), AIx standardized to heart rate 75 (AIx(HR75)) and PWV. Glomerular filtration rate (GFR) was measured by the <sup>51</sup>Cr-EDTA plasma clearance method. Statistical comparisons were made with t tests and multiple linear regression analysis. Results: GFR was the same in the two groups. Brachial diastolic blood pressure was slightly but significantly higher in ADPKD patients than in controls (81 ± 9 vs. 73 ± 9 mm Hg, p < 0.05). No significant difference was present in brachial systolic blood pressure. AIx was significantly higher in ADPKD than in controls: 21.6 ± 11.3 vs. 11.4 ± 11.2%, p < 0.02. AIx(HR75) and estimated aortic systolic and diastolic blood pressure was likewise significantly higher in ADPKD than in controls. Multiple linear regression analysis showed AIx and AIx(HR75) to be independently correlated to group (ADPKD/control), p < 0.02 and p < 0.05, respectively. No difference was found between PWV in the two groups. Conclusion: Reflection of the pulse wave was amplified in young normotensive ADPKD patients, demonstrating early pathology in the arterial system.