While duplex scanning has been advocated as the most accurate modality for postoperative graft surveillance, it is time-consuming for evaluating the entire graft. The aim of the present study was to determine which parameter predicts graft failure most simply and precisely, by examining 62 men and 1 woman who collectively underwent 71 infrainguinal arterial bypasses. A total of 212 scannings were obtained using a duplex scanner, and the peak systolic velocity (PSV), PSV ratio, and peak-to-peak pulsatility index (PPI) were analyzed. This analysis revealed 7 occlusions, 9 stenoses, and 1 arteriovenous fistula. When a PSV < 45 cm/s and/or a PSV ratio > 2.0 was defined as graft failure the sensitivity was 84.0% and the specificity was 81.8%: however, a PPI < 7.0 at the midgraft, indicating graft failure, showed a sensitivity of 100% and a specificity of 83.3%. The PPI exhibited better sensitivity and specificity than the PSV, even though the PPI needs only to be measured at the midgraft whereas the PSV should be measured at at least two points. Thus, we believe that the PPI could be the most useful and simple parameter to assess infrainguinal bypass grafts.