Synovial osteochondromatosis is a rare benign pathology arising from the synovial membrane of the joints, synovial sheaths or uncommonly the bursae around the joints. Baker's cysts are fluid filled, synovium-lined lesions arising in popliteal fossa. Synovial chondromatosis involving the Baker`s cyst is extremely rare. The aim of this case report is to document this exceedingly rare extra articular synovial pathology involving Baker's cysts of bilateral knees and to emphasize the importance of radiographs and sonography in the diagnosis.