Temporomandibular joint (TMJ) ankylosis is characterized by bony fusion that limits TMJ mobility. We present the case of an elderly woman who was brought to the operating room for dental rehabilitation under general anesthesia. The patient had an undiagnosed TMJ ankylosis, which was discovered only after induction of anesthesia due to her nonverbal status and advanced dementia. The surgical team canceled the case due to limited access to the surgical field. We discuss the factors that suggest TMJ ankylosis and propose the perioperative management when TMJ ankylosis is suspected but unconfirmed.