Dentigerous cysts are commonest type of developmental, epithelial-lined, odontogenic cysts arising in the jaw from the crowns of impacted, unerupted or embedded tooth, most often third molar. But dentigerous cysts arising from ectopic tooth in maxillary sinus is quite rare. Ameloblastoma changes in the dentigerous cysts are rare and to the best of our knowledge have not been reported to be arising from ectopic tooth in maxillary antrum. In this article, we present the radiological diagnosis, clinical features and management of this rare case of ameloblastic transformation in dentigerous cyst arising from ectopic tooth in maxillary antrum.