Synovial chondromatosis is an uncommon disorder characterized by cartilaginous proliferation within the synovial membrane of the articular joint. Smaller joints are rarely affected and it may be progressed to osteochondromatosis after ossification or calcification of metaplastic cartilage. It is commonly presented in the third to fourth decade of life, but rarely presented in adolescence. We report a unique case of synovial osteochondromatosis of the subtalar joint in 14-year-old baseball player. Arthroscopic removal of loose body and complete excision of the osteochondral mass with concomitant synovectomy resulted in satisfactory outcome without recurrence at final follow-up.