Approximately 99,000 infra-inguinal bypass procedures were performed in the U.S. in 1998. It is estimated that approximately 22% of all infra-inguinal bypass grafts will fail by 12 months. Graft failure rates have been estimated to increase to 40% at 12 months for patients receiving composite, cephalic or lesser saphenous (high-risk) vein grafts (Vascular Surgery Registry, Brigham and Women’s Hospital). These primary graft failures are typically due to stenoses that result from neointimal hyperplasia, a pathological adaptation process that occurs in veins exposed to the arterial circulation. The consequences of graft failure are as significant as those of primary atherosclerotic disease and include ischemia and poor wound healing that may result in amputation. Since the long-term patency of venous grafts can be improved with treatment prior to frank occlusion, considerable efforts have been focused on the methods for the detection of grafts at high-risk for failure. Duplex ultrasonography has been determined to be a sensitive screening test for the early detection of failing grafts. Peak systolic velocity (PSV), as measured by duplex ultrasound, has been shown to be a sensitive marker for low flow, and wave form analysis has permitted the identification of areas of stenosis in the vein under study. Management of patients who have undergone infra-inguinal bypass therefore includes routine surveillance with duplex ultrasound and the immediate correction of significant (more than or equal to 70%) graft stenoses.