Tracheomalacia is characterized by the collapse of the tracheal wall due to the softening of the tracheal cartilage and myoelastic tissues. We describe the case of a 12-year-old morbidly obese boy, without previous medical issues, scheduled for elective laparoscopic cholecystectomy. Immediately after pneumoperitoneum was established, mechanical ventilation could not be performed. Intraoperative exploration with flexible bronchoscopy showed that the tip of the endotracheal tube was nearly occluded by the posterior tracheal wall bulging anteriorly. Anesthesiologists should be aware of undiagnosed tracheomalacia as a cause of sudden airway collapse, even after the airway is secured with an endotracheal tube.