We present a case of problematic tracheal intubation in an adult patient with an unrecognized tracheal bronchus. Immediately after tracheal intubation and position change to prone, bilateral breath sounds were almost absent, and there was a diminished tidal volume. In order to resolve the ventilatory difficulty, the wire-reinforced tube was replaced with a conventional tube, and proper positioning of the tube was completed under fiberoptic guidance. A tracheal bronchus (originating about 1.2 cm above the carina, and supplying the right upper lobe) was found on the postoperative chest CT. In the presence of tracheal bronchus, tracheal intubation may cause pulmonary complications. Anesthesiologists should keep in mind the anesthetic implications of tracheal bronchus, and must be familiar with the use of fiberoptic bronchoscopy for proper positioning of endotracheal tube.