The lateral periodontal cyst is a rare odontogenic cyst of developmental origin. It occurs on the lateral periodontal region of a vital tooth and has specific histologic features. In this paper a case of a lateral periodontal cyst is presented and cases previously reported in the literature are reviewed. The present case concerns a 50-year old woman who presented for an asymptomatic gingival swelling of the left canine mandibular region of 2 month's duration. X-ray examination showed a well circumscribed radiolucency with a radiopaque margin lying between the roots of the lateral incisor and canine. The associated teeth were vital. Enucleation of the lesion was performed. The histologic examination of the specimen showed a cyst lined by thin non-keratinized epithelium with focal thickenings containing clear cells.