Epithelial odontogenic tumors arise from odontogenic epithelial structures. Malignant epithelial odontogenic tumors are extremely rare. Ameloblastic carcinomas may present denovo, ex ameloblastoma or ex odontogenic cyst. Most ameloblastic carcinomas are presumed to present denovo. To date less than 45 cases of ameloblastoma with metastasis have been reported. It occurs primarily in the mandible in a wide range of age groups; no sex or race predilection has been noted. It may present as a cystic lesion with benign clinical features or as a large tissue mass with ulceration, significant bone resorption, and tooth mobility. The lesion is usually found unexpectedly after an incisional biopsy or the removal of a cyst. Histologic features of ameloblastic carcinoma shows tumor cells that resemble the cells seen in ameloblastoma, but they show cytologic atypia. Moreover, they lack the characteristic arrangement seen in ameloblastoma. The clinical course of ameloblastic carcinoma is typically aggressive, with extensive local destruction. Here we describe a rare case of ameloblastic carcinoma (secondary dedifferentiated carcinoma) of mandible in a 40-year-old female patient. Ameloblastic carcinoma: Secondary dedifferentiated carcinoma of the mandible.