['Paraoxanase 1 (PON 1) has been shown to protect against atherosclerosis by modifying lipoproteins. Its activity decreases in dialysis patients but is restored after transplantation. Whether it affects arterial stiffness is unclear. In this study we aimed to investigate the effects of PON 1 on arterial stiffness in renal transplant patients.', 'Seventy renal transplant recipients were enrolled. Arterial stiffness was measured using a Syphmocor device. PON-1 activity was assessed from the rate of enzymatic hydrolysis of paraoxon to p-nitrophenol.', 'Mean age was 39.0 ± 9.6 years and 5.7% of the patients were diabetic. Post-transplant follow-up time was 46.7 ± 37.9 months. Eighty-five percent received anti-hypertensive and 12.9% anti-hyperlipidemic medication. Mean PON1 activity was 75.9 ± 52.4 U/L. PON1 activity was negatively correlated with systolic and diastolic blood pressure, mean arterial pressure, LDL-cholesterol and carotid-femoral pulse wave velocity (cf-PWV). Mean c-f PWV was 8.10 ± 1.39 m/s. Cf-PWV was positively correlated with age, systolic and diastolic blood pressure, mean arterial pressure, proteinuria and negatively correlated with PON1, PON1/HDL ratio and creatinine clearance. In linear regression analysis, PON1 was a predictor of cf-PWV in a model that included age, gender, diabetes, mean arterial pressure, urine protein level, creatinine clearance and PON 1.'] Does serum paraoxonase 1 activity predict arterial stiffness in renal transplant recipients?