ABSTRACTSynovial osteochondromatosis is an idiopathic benign metaplasia of the synovial membrane rarely found in an extra‐articular bursa. We describe the case of a 55‐year‐old woman with synovial osteochondromatosis in the subacromial bursa mimicking calcific tendinitis. Plain radiographs showed a radiopaque mass over the middle facet of the greater tuberosity, suggesting calcific tendinitis. Sonography, however, showed a loose body in the subacromial bursa, and no evidence of calcification inside the rotator cuff. © 2013 Wiley Periodicals, Inc. J Clin Ultrasound 42:237–240, 2014