This report describes a neoplasm involving the adrenal cortex of an aged female African clawed frog (Xenopus laevis). The animal was found to be in poor body condition and was subsequently euthanized. At necropsy, a 31.1 × 26.0–mm firm abdominal mass was identified near the left ovary. Concurrent hemoabdomen was present, as well as multiple adhesions to the small intestine. Histologic examination revealed a well-circumscribed, pseudoencapsulated, densely cellular, polygonal cell neoplasm arranged in either large solid swaths separated by dense fibrous connective tissue, or in looser nests, islands, and infrequent trabeculae. In the former arrangement, cells occasionally form small tubular structures or rosettes, within which is often an amorphous to granular eosinophilic material. In the latter, the cells palisade along the external limit of the islands, which are separated by wide channels of loose collagen, fibrin, and edema. Ultrastructurally, neoplastic cells were noted to have a centrally placed nucleus with peripheralized heterochromatin, a single nucleolus, numerous fusiform mitochondria with tubular cristae, and mildly osmiophilic lipid droplets, which is consistent with, although not diagnostic of, adrenal adenoma. Spontaneous tumors in amphibians are rare, and this is the first report of an adrenal adenoma in X. laevis.