Synovial cysts of the temporomandibular joint are rare. They commonly occur in the wrist, knee and feet. The main symptoms of synovial cysts occurring in the temporomandibular joint include preauricular pain and swelling, and surgical removal is the gold-standard treatment. A 54-year-old woman who presented with swelling of the right temporomandibular joint visited Kyungpook National University Dental Hospital. She had undergone enhanced computed tomography from another hospital, which showed a 1.1 × 0.8 × 1 cm well-defined rounded cystic lesion on the lateral area of the right temporomandibular joint. A synovial or ganglion cyst was suspected. The cystic lesion was surgically removed under general anesthesia and was histopathologically diagnosed as a synovial cyst. Histopathological findings show a lumen surrounded by loose fibrous tissue, and the lining is in a folded form and is composed of synovial cells.