The objective of this study was to evaluate hemodynamic variables in arteriovenous fistulas by color Doppler ultrasonography. This study involved 28 patients with chronic renal failure who were sent to surgery clinic for creation of an arteriovenous fistula of the Brescia-Cimino type. Patients were evaluated preoperatively and on the first and seventh days postoperatively by a color Doppler ultrasound machine with a 7.5 MHz linear probe. The distal radial artery was examined preoperatively and the fistula itself postoperatively. Changes in the fistula size and the velocity, volume, and resistive index of the distal radial artery were recorded. Postoperatively the radial artery diameter, systolic flow rates, and volume flow had increased significantly, especially on the first day, in comparison to preoperative values. Resistive index values has deceased significantly at both the first and the seventh days postoperatively. Color Doppler ultrasonography is a very effective method in the evaluation of hemodynamics of arteriovenous fistulas in hemodialysis patients. It will allow an understanding of the pathology in nonfunctioning fistulas or of the cause of complications that develop secondarily.