OBJECTIVES: Arterial stiffness is recognized as an independent risk factor for cardiovascular morbidity and mortality. Recent studies found that osteoprotegerin (OPG) is associated with arterial stiffness and may reflect endothelial dysfunction. The aim of this study was to evaluate the relationship between fasting serum OPG levels and the aortic augmentation index (AIx) in renal transplant recipients. MATERIALS AND METHODS: Fasting blood samples were obtained from 66 renal transplant recipients. The aortic AIx was measured using a validated tonometry system (SphygmoCor). Serum OPG levels were measured using a commercial enzyme-linked immunosorbent assay kit. RESULTS: Univariate linear analysis of the aortic AIx in renal transplant recipients revealed that body fat mass ( = 0.377, = 0.002), aortic diastolic blood pressure (DBP; = 0.307, = 0.020), triglycerides ( = 0.260, = 0.035), and logarithmically transformed OPG (log-OPG, = 0.402, < 0.001) were positively correlated, whereas height ( = 0.361, = 0.004) and body weight ( = 0.212, = 0.041) were negatively correlated with the aortic AIx in renal transplant recipients. Multivariate forward stepwise linear regression analysis of the factors significantly associated with the aortic AIx showed that log-OPG ( = 0.213, < 0.001), height ( = 0.081, = 0.009), and aortic DBP ( = 0.058, = 0.022) were independent predictors of the aortic AIx in renal transplant recipients. CONCLUSION: These results suggest that the serum fasting OPG level is associated with the aortic AIx in renal transplant recipients.