Lower extremity computed tomography angiography (CTA) is frequently used for anatomic assessment of lower extremity peripheral arterial disease. When lower extremity bypass is planned, duplex ultrasound (DUS) is routinely obtained to evaluate the great saphenous vein (GSV) for use as conduit. Although GSV can be visualized on CTA images, diameter assessment is not routinely included in formal study interpretation. We hypothesized that CTA images could be used to measure GSV diameters and that CTA-based diameters would correlate with measurements obtained using DUS.