A case of ankylosing elbow with unusual ossification was reported. The patient was a twenty-seven years old female who had an episode of inflammatory sign over the arm about three years ago. On X-ray examination, the ossification was extraarticular and localized only in the fan-like part of medial collateral ligament of the elbow. The abnormal ossification was thought to be attributed to the fibrositis ossificans circumscripta. After resection-arthroplasty of the ossified bony bridge, the patient recovered satisfactory range of motion of the elbow.
