The aim of this study was to evaluate whether preoperative color Doppler ultrasonography improves immediate success rates of arteriovenous fistulas for dialysis. One hundred twenty-four patients with chronic renal failure underwent color Doppler ultrasonographic examination of both arms, including the cephalic vein, before arteriovenous fistula construction. Patients were randomly divided into 2 groups: A and B. In group A, there were 52 patients, and the surgeon planned to construct arteriovenous fistulas depending only on physical examination. In group B, which comprised 72 patients, surgeons performed arteriovenous fistula construction on sites labeled by color Doppler ultrasonography. In group A, of 52 patients who had surgery for arteriovenous fistula construction, 13 had fistulas that did not function. Among these 13 patients, 8 were found to have chronic thrombotic changes in the cephalic vein on color Doppler ultrasonography, and 5 had none of these changes. When we checked the color Doppler ultrasonographic findings, we noted that these 5 patients had decreased volume flow in the radial artery. On the whole, the arteriovenous fistulas worked in 39 patients (75%) and did not function in 13 patients (25%). In group B, surgeons followed the color Doppler ultrasonographic results. Of 72 patients who underwent the procedure, 68 patients (94.4%) had functioning fistulas, whereas 4 (5.6%) had fistulas that did not work. These 4 patients were found to have low volume flow in the radial artery. When both groups were compared by chi2 analysis, the difference was statistically significant (P = .002). Group B, in which patients were preoperatively evaluated by color Doppler ultrasonography, had a high success rate. We found that color Doppler ultrasonography is very helpful as a noninvasive procedure for this evaluation. Although many surgical clinics still perform arteriovenous fistula construction without the aid of color Doppler ultrasonographic findings, we think that the use of color Doppler ultrasonography should be emphasized before surgeons proceed with arteriovenous fistula construction.