This report describes a case of orthokeratinized odontogenic cyst arising in the mandibular molar region of a 39-year-old man. Under the initial clinical diagnosis of radicular cyst, root canal treatment was performed on the mandibular right second molar. The treatment that continued for six months did not achieve healing. Subsequently surgical intervention was selected since the tooth fracture was found, and the prognosis was judged to be poor. After atraumatic tooth extraction, the apical cystic lesion was enucleated, and the tooth was replanted. A definite diagnosis of orthokeratinized odontogenic cyst was made by histopathological examination of the biopsy specimen. The radiograph taken seven months after the operation showed an improvement in the radiolucent lesion. No clinical signs of tooth mobility, pain, and swelling were present. The tooth was then successfully retained with the final restoration. Careful follow-up is needed in order to detect any signs of recurrence.