Sleep apnea syndrome is a relatively common disorder characterized by periodic cessation of breathing during sleep because of upper airway obstruction (obstructive sleep apnea) or by reduction of ventilatory drive (central sleep apnea). We report the case of a middle-aged, obese man who underwent tracheostomy for the treatment of obstructive sleep apnea documented by polysomnography. Although tracheostomy resulted in marked clinical improvement, relief of upper airway obstruction unmasked severe central sleep apnea. We report the successful treatment of this patient's central sleep apnea syndrome with the use of supplemental CO2 therapy.