Severe upper airway obstruction due to thyroid cancer is often related severe hypoxia and hypercarbia during anesthesia induction. Attempts to insert an endotracheal tube or a bronchoscope may cause complete immediate airway obstruction. We anesthetized two patients. One had a large mediastinal thyroid mass which compressed trachea and caused near complete obstruction, and the other patient had a large papillary thyroid cancer, which had invaded larynx and compressed the upper trachea. Patients were sedated with fentanyl 150 µg i.v. and a target controlled infusion (TCI, 1.8 µg/ml) of propofol. A femorofemoral cardiopulmonary bypass was performed under local anesthesia. After bypass, the propofol TCI concentration was increased to 3.5 µg/ml, and fentanyl 500 µg and vecuronium 6 mg were injected. Ventilation was performed using a laryngeal mask in one patient, and a laryngeal tube in the other. After removing the tumor mass, the airway was secured, and the cardiopulmonary bypass discontinued. All patients recovered uneventfully and were discharged. We discuss the management of severe upper airway obstruction and the usefulness of cardiopulmonary bypass.