The frequency of epidermoid cysts in the maxillofacial region is relatively low. Reported: a case of a giant sublingual epidermoid cyst on the floor of the mouth. Case: 38-year-old woman. Chief complaint: oral swelling and respiratory distress. History of present illness: no special notes. Current medical history: she was aware of swelling of the floor of the mouth six months before visiting our department and was referred to our department because of increasing size. Present symptoms: at the time of examination, forced respiration and dysarthria were observed and a spherical soft elastic and well-defined mass was observed on the floor of the mouth. Due to the lesion, the tongue was displaced to the pharyngeal side and the tip of the tongue could not be confirmed. Imaging tests revealed a 65 mm × 76 mm × 54 mm well-defined mass on the mylohyoid muscle, and a dermoid or epidermoid cyst was suspected. Based on the clinical diagnosis of the cyst, the bulk of the cyst contents was reduced under general anesthesia, and the cyst was removed by intraoral surgery. The pathological diagnosis was an epidermoid cyst. For sublingual giant epidermoid cysts, removal by content reducing surgery was considered to be effective.