A regional anesthetic technique formerly used in adults for tonsillectomy was adapted to provide posttonsillectomy pain relief in children. Injection of 3-10 mL of 0.25%-0.5% bupivacaine into each lateral pharyngeal space appeared to provide good postsurgical analgesia. A retrospective chart review failed to link the technique to airway-related complications. A prospective, randomized, double-blind, placebo-controlled trial comparing the analgesic effectiveness and postsurgical complications in patients undergoing tonsillectomy and receiving either bupivacaine or placebo was begun after institutional approval and informed consent. The study was terminated after eight children had been enrolled because two of four children receiving bupivacaine developed severe upper airway obstruction (UAO) after extubation of the trachea. We conclude that the volume and concentration of bupivacaine were sufficient to block the vagus nerves proximal to the take off of the recurrent laryngeal nerves and/or the hypoglossal nerves, resulting in severe UAO. The short distance between the hyoid and jugular foramen would predispose children and adults with a short neck to the development of this complication. In conclusion, bilateral local anesthetic injection into the lateral pharyngeal space may result in severe UAO and loss of protective reflexes.