A 9 year-old intact Duroc sow presented to the Cornell University Hospital for Animals with a 5 week history of bloody vaginal discharge, weight loss, and weakness. Transrectal ultrasound demonstrated swirling, anechoic uterine fluid. Exploratory celiotomy revealed a non-resectable uterine mass, and the patient was euthanized. At gross postmortem examination, a 13x11x5cm, multilobulated, highly infiltrative mass expanded the wall of the left uterine horn and broad ligament. In multiple areas, the mass was associated with endometrial ulceration. A second, 4x3x2cm firm, white, encapsulated mass was identified in the right uterine horn. Diffuse, severe cystic endometrial hyperplasia was present in both uterine horns. On histologic examination, the mass from the left uterine horn was an adenocarcinoma with a marked scirrhous response. The mass from the right uterine horn was a leiomyoma. Uterine adenocarcinoma is rare in the pig, and this is first case report of adenocarcinoma occurring consurrent with leiomyoma.