A yearling, warmblood colt presented for a several month history of swelling over the left withers with intermittent drainage. Previous management by the referring veterinarian was unsuccessful. On presentation, the left withers was swollen and had two draining tracts. After radiographs ruled out bone involvement, ultrasound was used to map the draining tracts for surgical debridement. Standing surgery was planned, but aborted because the correct level of analgesia/sedation could not be achieved in this patient. He was placed under general anesthesia and a dorsally attached skin flap was created to provide access. The infected tissue, the supraspinous bursa, as well as part of the nuchal ligament were debrided and the skin flap temporarily closed. The day after surgery the skin flap was reopened, flushed, and packed with gauze. The flap was closed using both loops on each side of the incision placed during surgery and umbilical tape. The flap was managed daily to establish drainage and healing. Ultimately the flap healed down to the body wall but a few months post-surgery another draining tract was discovered.