A case of a rare odontogenic cyst arising in the lateral periodontal membrane in the mandible in a 14 year old girl is reported. This lesion appeared to be a new entity and has been named glandular odontogenic cyst (GOC) or sialo-odontogenic cyst. Histologically the lesion was lined by mucous producing cuboidal epithelium containing several areas of thickening and numerous duct-like structures. The cyst recurred with the same histology two years postoperatively.