Scimitar syndrome is a rare complex of congenital anomalies of the cardiopulmonary system. In patients with scimitar syndrome, the right pulmonary vein abnormally drains into the inferior vena cava, right atrium, coronary sinus, azygos vein, portal vein, or hepatic vein. The syndrome gets its name from the Turkish sword-like image that appears on chest x-ray. Some patients with scimitar syndrome survive in adulthood undiagnosed. Herein, we discuss positional oxygenation and hemodynamic changes associated with scimitar syndrome, especially in the left lateral decubitus position, detected during preoperative anesthetic examination in an adult patient who underwent general anesthesia for left mastectomy.