A 65-year-old man presented with a subcarinal mass incidentally found during the preoperative work up for bladder cancer. Magnetic resonance imaging revealed a circumscribed mass suggesting a bronchogenic cyst. After completing a trans-urethral resection of bladder cancer, he was referred to our department and planned to undergo a surgical resection of the tumor. The patient was placed in the prone position and his right arm was raised cranially. Under one-lung ventilation, the initial 5-mm port was inserted at the fifth intercostal space (ICS) on the right middle axillary line (port 1, Fig. ). CO2 was insufflated through this port at a pressure of 8 mmHg. Under a thoracoscopic view, the second 5-mm port and third 12-mm port were inserted at the ninth ICS on the scapular line (port 2) and seventh ICS on the middle axillary line (port 3), respectively. With the thoracoscope inserted through port 2, the surgeon held a grasper and electrocautery via port 3 and port 1. In addition to CO2 insufflation, a gravity effect also facilitated the exposure of the posterior mediastinum and subcarinal mass wide enough without any retraction. The mediastinal pleura was incised inferiorly to mobilize the tumor from the pericardium and bronchus. However, 10 min after beginning the surgery, he required bilateral ventilation because of hypoxemia when his O2 saturation dropped to 81% probably caused by diaphragmatic compression (his body mass index was 25.3). Nevertheless, the operative field was maintained excellently even with bilateral ventilation and we completed the total resection of the tumor successfully. The operative time and estimated blood loss were 126 min and 1 g, respectively. A histological examination revealed that the cyst wall lined by pseudostratified ciliated epithelium contained smooth muscle, consistent with a diagnosis of a bronchogenic cyst. The postoperative course was uneventful, and he was discharged 3 days after surgery.