We report a case of thymoma presenting superior vena cava syndrome. Anesthesia for biopsy or excision of an anterior mediastinal mass has been associated with major airway and cardiac complications. Therefore, careful anesthetic management is necessary. The patient was kept on Fowler's position, and anesthesia was induced with thiamylal. The patient was intubated with succinylcholine and allowed to breath spontaneously until the sternal incision. Thereafter we used vecuronium and controlled ventilation was maintained. Intraoperatively, arterial pressure, central venous pressure, and right- and left-brachiocephalic vein pressures were monitored. After bypasses between right atrium and right- and left-brachiocephalic vein had been made, the venous pressures decreased remarkably. Various methods for preventing side effects resulted in good control during the perioperative period.