Zee, a six year old male intact Great Pyrenees dog, was successfully treated with megavoltage radiation therapy for acanthomatous epulis located along the rostral mandible. Acanthomatous epulis is a nonmetastatic oral tumor of periodontal origin which is characterized by a cauliflower-like appearance, rapid growth, and a local invasiveness that nearly always involves infiltration into alveolar bone. Histologically, acanthomatous epulis frequently resembles the periodontal ligament, with broad chords of epithelium within a stroma of connective tissue. Radiation therapy and radical surgical excision are the primary modalities utilized for the treatment of acanthomatous epulis. Both treatment options provide excellent long term control of the neoplasm and are generally curative procedures. Controversy has existed regarding the formation of malignant neoplasms following irradiation of acanthomatous epulis. Recent information suggests that the use of megavoltage, rather than orthovoltage radiation, favors a very low incidence (3.5%) of radition-induced neoplasms. Because of the low probability for malignant tumor formation following megavoltage irradiation of acanthomatous epulis, the risk of developing a secondary neoplasm in the irradiation site is not a viable argument for declining to treat a patient with radiation therapy.