Ameloblastoma is a true neoplasm of odontogenic epithelial origin. Unicystic ameloblastoma refers to those cystic lesions that show clinical, radiographic or gross features of a mandibular cyst, but on histologic examination show a typical ameloblastomatous epithelium lining part of the cyst cavity with or without luminal and/or mural tumor growth. It accounts for 5 to 15% of all intraosseous ameloblastomas. They believed to be less aggressive and respond more favorably to conservative excision than the solid or multicystic ameloblastomas. We report a case of unicystic ameloblastoma of the anterior part of the mandible that was treated by enucleation and use of Cornoy's solution under suspicion of an odontogenic cyst. The nature of the lesion became evident only when the enucleated material was available for histologic examination. With this report, we illustrate the importance and complexity of a differential diagnosis of lesions with a cystic aspect in the anterior region of the mandible, among them are dentigerous cyst, odontogenic keratocysts, adenomatoid odontogenic and unicystic ameloblastoma.