A case of oral fibrosarcoma in a 13-yr-old male black iguana (Ctenosaura pectinata) is reported here. The iguana exhibited new tissue formation involving a large part of the maxilla and hard palate, which histologically and ultrastructurally corresponded to a primary fibrosarcoma of the oral cavity. Although there are reports of fibrosarcomas in other reptiles, such as snakes and crocodiles, no reports of this neoplasm in the oral cavity of an iguana were reported, which suggests that it is either infrequent or infrequently sampled for histological diagnosis. As an isolated case in an adult iguana living at a conservation center, it is likely that this diagnosis is associated with advanced age. The prognosis is considered unfavorable.