Lateral periodontal cyst （LPC） can rarely cause a loss of cortical bone in the jaws. We report cases of LPC and odontogenic keratocyst that showed similar clinical findings. Case 1 involved a 70-year-old woman who presented with gingival swelling in the right mandibular molar region. CT showed clear bone resorption in the right mandibular molar region, absorption of buccal cortical bone, and progression of the lesion beyond the bone. Cystectomy was performed under local anesthesia. Pathological findings revealed clear cells, and LPC was diagnosed. Case 2 involved a 40-year-old man who presented with gingival swelling in the lower premolar region. Buccal cortical bone of the right mandible absorbed on CT, and the lesion that resorbed the buccal cortical bone spread to surrounding soft tissues. Cystectomy was performed under general anesthesia. Pathological findings revealed lining epithelium comprising thin, parakeratotic, stratified squamous epithelium and columnar cells arranged in a palisade pattern in the basal layer. As of 2 years 6 months and 2 years 2 months postoperatively, respectively, neither case showed any evidence of recurrence.
