An adult racing pigeon (Columba livia) was presented with a subcutaneous mass on the ventral aspect of the right wing. A fine-needle aspirate and radiographic study of the mass were suggestive of highly invasive sarcomatous neoplasm. Euthanasia was decided because of the poor prognosis. Necropsy confirmed the highly invasive nature of the neoplasm, which also occupied a large portion of the right breast. There also was extensive osteolysis of the sternum with neoplastic invasion of the left breast and the coelomic cavity. Histopathology revealed a highly cellular, poorly demarcated, unencapsulated invasive sarcoma. Immunohistochemistry was positive for muscle actin, and myoglobin, weakly positive for vimentin, and negative for desmin, neuron-specific enolase and S-100 protein, suggesting a diagnosis of undifferentiated rhabdomyosarcoma.