Although synovial chondromatosis occurs frequently near the ends of long bones, such as the knee, elbow, and hip joints, it rarely affects the temporomandibular joint.<BR>A 52-year-old woman visited our hospital because of swelling in the left side of the temporomandibular joint and trismus. On magnetic resonance imaging, the lesion was found to be chondroid tissue between the left mandibular fossa and the condylar head. Magnetic resonance imaging revealed a high signal mass measuring 35×40mm around the left condylar head. The clinical diagnosis was synovial chondromatosis. Synovectomy and removal of the mass were performed with the patient under general anesthesia. Histopathologically, the mass was formed by typical chondrocytes and was diagnosed to be synovial chondromatosis. The patient has been followed up for 1 year 4 months. There has been no reccurence of the mass or temporomandibular joint disorder.