Microsurgical procedure of free tissue transfer in critical limb ischemia patients with large ulceration has already been established. The nutrient flap concept was that transferred tissue functioned not only to cover the skin defect but also as a supplementary blood supply to the ischemic lower leg. This report showed the justification for this concept, which was rarely discussed. A 58-year-old male patient with progressive forefoot gangrene caused by arteriosclerosis obliterans was presented. The distal bypass procedure was performed as revascularization surgery, and a latissimus dorsi (LD) myocutaneous flap was transplanted to cover ulceration. The arterial pedicle of the flap was anastomosed to the vein graft in an end-to-end manner, and the venous pedicle was anastomosed to the posterior tibialis vein in an end-to-end manner. Bypass graft blood flow went straight to the LD flap only. The postoperative course was uneventful. The free flap and right foot survived successfully and the patient was ambulatory with no recurrence of ulceration wearing order-made shoes more than three years after transplantation. Vessel-selective angiography was performed two months after surgery. An angiographic catheter was inserted into the bypass graft, which ran straight through the flap nutrient artery. The results obtained showed that not only the transferred flap area, but also the remaining original foot soft tissue (including the sole and heel) was clearly visualized radiologically only through the flap nutrient vessel. This findings of the angiography appear to provide direct evidence for the nutrient flap concept.