We report a case of painless synovial chondromatosis with an extremely large mass at the popliteal area related to the right knee joint. A hard mass at the posterior aspect of the knee was the only complaint reported by the patient. Plain X-ray studies revealed punctuated calcifications both intra-articularly and around the knee joint. With the surgical procedure performed subsequently, multiple rocky-hard giant chondroid nodules were excised from the posterior aspect of the knee. After 9 months following the surgery, the patient had full range of motion, and no complaints. We emphasize on the importance this case because these lesions may simulate tumors, and lead to misdiagnosis.