A case of acute intraoperative hypoxemia following placement in the lateral decubitus position in a chronic diaphragmatic hernia patient undergoing general anesthesia for hip arthroplasty is presented. The patient had previously received a series of transurethral cystectomies under general anesthesia without any pulmonary complications, even though the patienthad a diaphragmatic hernia. Hypoxemia occurred after the induction of anesthesia and reposition, and surgery was subsequently postponed. The mechanisms proposed for the hypoxemia were a progressive compression atelectasis of the dependant lung caused by placement in the lateral decubitus position and the presence of the diaphragmatic hernia during anesthesia, and further reduction of the FRC of the dependent lung caused by mechanical ventilation. The patient was intubated with a left-sided endobronchial tube. After placing the patient in the lateral decubitus position, intermittent passive hyperinflation to the dependent lung and then positive pressure ventilation of both lungs was maintained to provide adequate oxygenation throughout the surgery. Therefore, differential ventilation using a double lumen tube is effective at improving hypoxemia of a patient in altered pulmonary compliance, such as in the lateral decubitus position with adiaphragmatic hernia.