A cementoblastoma is rare, benign, and of odontogenic ectomesenchymal origin, usually associated with the roots of the first mandibular tooth. We present an unusual case of one that involved the roots of the first and second maxillary molars, extended into the maxillary sinus, and was associated with a displaced unerupted third molar. The initial presentation was misleading and resulted in inadequate management. The definitive diagnosis had not been established until 2 years later.