Ameloblastic carcinoma is a rare malignant lesion with characteristic histologic features and behavior that dictate a more radical surgical approach than does a simple ameloblastoma. Clinically, ameloblastic carcinoma is more aggressive than most typical ameloblastomas with extensive local destruction, perforation of the cortical plate, extension into surrounding soft tissues, numerous recurrent lesions, and metastasis, usually to cervical lymph nodes. The radiographic appearance of ameloblastic carcinoma is consistent with that of ameloblastoma except for occasional presence of some focal radiopacities, apparently reflecting dystrophic calcification. Histologically, the tumor cells resemble cells seen in ameloblastoma but show cytologic atypia, cellular pleomorphism, nuclear hyperchromatism, mitoses, and vascular and neural invasion. These identifying features of ameloblastic carcinoma must be known and recognized by dental practitioners. It is probable that ameloblastoma, like other tumors (such as carcinoid tumors and epithelial tumors of the ovary), shows a spectrum of histologic and biologic behavior ranging from benignity at one end to frank malignancy at the other. A case of ameloblastic carcinoma of the maxilla in a 70-year-old man is reported. Schlagwörter: ameloblastic carcinoma, ameloblastomas, tumors