Ameloblastoma is a common odontogenic tumor originating from the dental lamina, reduced dental epithelium and rests of Malassez, and represents 10% of all odontogenic tumors of the jaw. Unicystic ameloblastoma is normally encountered in young patients, and often occurs in the mandible, and is particularly associated with an impacted tooth. We encountered an unicystic ameloblastoma arising from a dentigerous cyst after the treatment of a radiolucent lesion on the mandible.