A 15-year-old, female Vieilott's fireback pheasant (Lophura rufa) presented with a 2-day history of a drooping right wing. Examination revealed severe soft tissue swelling in the area extending from the right shoulder to the humeral-radio-ulnar joint with associated bruising and feather loss. Results of a complete blood cell count revealed marked heterophilia and lymphocytosis, and results of serum biochemical analysis showed severe increases in creatine kinase and aspartate aminotransferase activities, hypoproteinemia, and hypoalbuminemia. Radiographs revealed osteolytic lesions of the right humerus with pathologic fractures and circumferential soft tissue swelling. Although surgical wing amputation was successful, the bird died the next day while being treated. The mass was diagnosed histologically and immunohistochemically as a leiomyosarcoma. This is the first neoplasia of any kind reported in this species, to our knowledge, and one of the very few reports of smooth muscle neoplasms affecting the limb of a bird.