Abstract-Aortic stiffness and chronic kidney disease are closely linked by shared risk factors and associated increased cardiovascular mortality. At lower levels of renal function, aortic stiffness is independently associated with glomerular filtration rate. However, the longitudinal impact of aortic stiffness on renal function has not been reported previously. A cohort of 133 patients with chronic kidney disease stages 3 and 4 (estimated glomerular filtration rate: 15 to 59 mL/min per 1.73 m 2 ) underwent prospective measurement of arterial stiffness parameters and monitoring of renal function. Aortic pulse wave velocity measurement was performed in 120 patients. The mean age was 69Ϯ12 years (meanϮSD; 103 men, 30 women, and 23.3% diabetic). Mean systolic blood pressure was 155Ϯ21 mm Hg, and mean diastolic blood pressure was 83Ϯ11 mm Hg. The mean Modification of Diet in Renal Disease estimated glomerular filtration rate was 32Ϯ11 mL/min per 1.73 m 2 . Change in renal function was measured using reciprocal creatinine plots and the dichotomous combined end point of Ն25% decline in renal function or start of renal replacement therapy. After stepwise multivariate analysis, aortic pulse wave velocity was independently associated with gradient of reciprocal creatinine plot (rϭ0.46; Pϭ0.014). In multivariate analysis of the end point of Ն25% decline in renal function or start of renal replacement therapy, independent predictors were aortic pulse wave velocity (rϭ0.48; Pϭ0.002), systolic blood pressure (rϭ0.17; Pϭ0.039), and urine protein:creatinine ratio (rϭ0.20; Pϭ0.021). We, therefore, conclude that aortic stiffening is independently associated with rate of change in renal function in patients with chronic kidney disease stages 3 and 4. (Hypertension. 2010;55:1110-1115.) Key Words: aorta Ⅲ pulse pressure Ⅲ microvessels Ⅲ kidney Ⅲ creatinine Ⅲ pulse pressure Ⅲ renal insufficiency C hronic kidney disease (CKD) is a common condition, affecting 10% to 13% of the population of the United States, 1 associated with a dramatically increased cardiovascular (CV) mortality, which increases with severity of renal impairment. This excess CV risk is in part attributed to an increase of traditional risk factors among people with CKD 2 but may also relate to the complex metabolic and vascular changes of CKD, including arterial stiffening. Aortic stiffness increases progressively as renal function declines 3 and has been independently associated with CV mortality in patients with renal failure. 4,5 Although much research has investigated the role of aortic stiffening in the causation of CV disease in patients with CKD, less attention has been paid to its potential etiologic role in the causation and progression of renal impairment. Aortic stiffening causes increased systolic blood pressure (BP; SBP) and widened pulse pressure (PP), both factors associated in longitudinal studies with increased rate of decline of renal function. 6,7 In addition, aortic stiffening results in loss of the dampening of ventricular ejection and could lead ...