Duplex sonography was used to assess functional features of arteriovenous fistula (AVF) for hemodialysis (HD). Internal diameter (ID), resistance index (RI) and blood flow (BF) velocity in feeding artery and in vein ofAVF, and venous BF volume were analyzed with purpose to determine the normal values. Presumed normal BF velocities are those of clinically well functioning shunts, allowing BF through HD lines of minimally 250 ml/min. Study included 66 nondiabetic HDpatients (30 women, 36 men), mean age 52-13 years, treated by HD for median 61 (4-252) months. Measurements in 47patients with clinically well functioning AVF were as followed: mean arterial ID 5.2 +/- 1.4 mm, median arterial RI 0.3 (0.3-0.9), median arterial BF velocity 1.5 (0.6-3.6) m/s, mean venous ID 7.6 +/- 2.2 mm, median venous RI 0.3 (0.3-0.9), mean venous BF velocity 1.6 +/- 0.7 m/s, and median venous BF volume 530 (120-1890) ml/min. Patients with poor functioning AVF had significantly less arterial ID, higher arterial RI, less venous ID, less venous BF velocity and volume. Duplex sonography findings obtained for clinically estimated well functioning shunt should be considered as normal Doppler values. Blood vessels' morphologic features depend upon age, and older patients have more pronounced changes.