We report a case of anastomotic failure secondary to acute vasculitis in a free flap. Following transfer of a latissimus dorsi myocutaneous flap, massive hemorrhage from the anastomosis occurred six days postoperatively. This was associated with segmental infarctions of the areas of the flap, which was removed. Transmural necrosis of the thoracodorsal artery, secondary to acute vasculitis was demonstrated by histology. Subsequent biopsies revealed an autoimmune vasculitis.