Dermoid cysts of the oral cavity usually present as a solitary, painless mass in the midline or, on occasion, more laterally in the submandibular region. A patient is described who presented with a mass in the submandibular region, which could be made to appear or disappear at will. This unusual manifestation occurred as the cyst plunged around the posterior border of the mylohyoid on tensing the floor of the mouth.
