The median mandibular developmental cyst is an extremely rare lesion. It has a disputed orgin.Recently, we experienced a case of a so-called median mandibular cyst which was doubted, and was diagnosed as a non odontogenic cyst based on the results of the clinical and histopathological evaluation. It was reported.The patient was a 45-year-old man who was reffered to us for evaluation of his X-ray radiolucency of the mandibular symphysis.The history of traumas to the lower jaw was not obtained from the patient.Upon routine examination, a slightly bulging, nontender nonfluctuant, hardmass was noticed on the labial surface in the lower anterior region of the mandible.Electric pulp testing revealed that the right central incisor was nonvital and other incisors were vital.Radiographs revealed a spheral-shaped radiolucency, 2 cm in diameter, at the midline of the mandible and separated the roots of the central incisor teeth. The clinical diagnosis was a developmcntal cyst.Under local anesthesia, the cyst was enucleated in toto. In surgical findings, the cyst wall had no connection with the roots of the teeth.Histopathological examination of the cyst wall showed it was lined by a stratified cilliated epithelium and fibrous connective tissue.One area of the cyst revealed the squamous metaplasia in the field of inflammation.