Prospective randomized multicenter comparison of in situ and reversed vein infrapopliteal bypasses. We have performed a prospective, randomized, multicenter study to compare in situ and reversed vein grafts for long limb salvage bypasses from the proximal thigh to an infrapopliteal artery. Three hundred eighty-four patients required an infrapopliteal bypass for critical lower extremity ischemia. Of these, 259 were excluded because a short vein bypass was performed or because the vein was considered inadequate. The remaining 125 patients had a randomized vein bypass, 63 reversed, 62 in situ. The two groups were similar with regard to risk factors, indications, graft dimensions, and outflow. Secondary patency at 30 months was similar for both techniques: reversed 67% +/- 9% (+/- SE); in situ 69% +/- 8%. For veins less than or equal to 3.0 mm in minimum distended diameter 24-month patency rates were 61% +/- 22% for 12 in situ veins and 37% +/- 29% for 10 reversed veins (p greater than 0.05). Angiographic evaluation of failing grafts revealed lesions similar in type and frequency in both types of grafts. These included focal (in situ, n = 4; reversed, n = 7) and diffuse vein hyperplasia (in situ, n = 2; reversed, n = 1), and inflow and outflow stenoses (in situ, n = 4; reversed, n = 3). The incidence of wound complications and the mortality rate were similar for the two groups. These data show no significant difference in overall patency rates for the two types of vein grafts at 2 1/2 years. 