Mucous cysts derived from heterotopic salivary tissue are rare, especially in the middle of the posterior of the tongue. We treated a case of mucous cyst that arose in an ectopic salivary gland in the middle of the posterior of the tongue. We report this case together with a literature review. A 21-year-old woman was referred to our hospital because of a painless swelling in the middle of the posterior of her tongue. Magnetic resonance imaging showed a well-circumscribed ovoid mass. The lesion extended from the posterior of the tongue to the left side of the floor of the mouth under the mucous membrane. A clinical diagnosis of a thyroglossal duct cyst was made, and the Sistrunk operation was performed. The pathological diagnosis was a mucous cyst. The patient’s postoperative course was uneventful, and there were no signs of recurrence during the 24-month follow-up period.
