Color flow image-directed Doppler ultrasound was used to image 9 iatrogenic arteriovenous (AV) fistulas in the groin following femoral artery catheterization. Characteristic findings in the color images and spectral waveforms seen in most patients included (1) visible connection between the artery and vein (8 cases); (2) a multicolored speckled mass at the fistula site (7 cases); (3) spreading of color pixels into the extraluminal soft tissues (7 cases); (4) high diastolic flow in the arterial waveform proximal to the fistula site (7 cases); (5) decreased flow in the artery caudal to the fistula (5 cases); and (6) high velocity turbulent flow, sometimes with a pulsatile component, in the vein near the fistula (9 cases). The authors conclude that color flow imaging is useful in differentiating an AV fistula from other complications of femoral artery catheterization, such as pseudoaneurysm or hematoma.