Mediastinal masses may cause life-threatening complications such as major airways obstruction, superior vena caval obstruction, and cardiac compression during general anesthesia. We present a case in which superior vena caval and airway obstruction developed at induction of anesthesia in a patient with an anterior mediastinal mass. Shortly after induction of anesthesia in the supine position, the patient became difficult to ventilate and blood began to flow upward into the IV line. The patient was immediately turned to the right lateral position and allowed to breathe spontaneously. The ventilation of patient was improved significantly and cyanosis of the face and upper extremities disappeared. We think that general anesthesia should be avoided if at all possible in patients with mediastinal mass and alternative methods of diagnosis and management are discussed.