A 26-year-old man presented to physical therapy for evaluation of right shoulder pain. While history and physical examination findings were most consistent with right shoulder impingement, a firm mass over the acromioclavicular joint was observed. Radiographs of the right shoulder revealed a soft tissue prominence adjacent to the acromioclavicular joint, while contrast-enhanced magnetic resonance imaging revealed a 9 × 16-mm soft tissue mass arising from the right acromioclavicular joint. The patient underwent incisional biopsy, acromioclavicular joint capsulotomy, and distal clavicle excision. Histological evaluation revealed hyalinized fibrovascular connective tissue with focal calcification but no hemosiderin (insoluble iron deposits), consistent with synovial chondromatosis. The patient returned to full activity without limitations postoperatively. J Orthop Sports Phys Ther 2011;41(2):118. doi:10.2519/jospt.2011.0403