A 9 year old female spayed mixed breed dog presented to Cornell’s Soft Tissue Service for evaluation of an intrathoracic mass visualized on thoracic radiographs. Thoracic CT and ultrasound were performed to further characterize the origin of the mass and define potential treatment options. The diagnostic workup revealed a mass arising from the left body was that was independent of other structures within the thoracic cavity. A thoracotomy was performed and complete excision of the mass was attained by removal of the associated 4th and 5th left ribs. Body wall reconstruction was achieved by using Mylar mesh. Post-operative care included intravenous analgesics and antibiotics and routine chest tube care. Surgical biopsy reported a low-grade sarcoma with complete excision.