Because of the increased intra-abdominal pressure and the physiologic changes in the obese patient, laparoscopic bariatric surgery can aggravate perioperative pulmonary complications. A 23-year-old female with morbid obesity experienced pulmonary edema after laparoscopic adjustable gastric banding surgery. One lung was unintentionally ventilated for approximately 5 minutes during the operation. At the end of the operation, profuse pink frothy sputum emerged from the left lung. The chest roentgenogram showed the atelectasis and severe edema in the left lung superimposed on diffuse interstitial bilateral pulmonary edema. After aspiration of the secretions and oxygen supplementation, the patient recovered uneventfully.