BACKGROUND: Laparoscopic and pelviscopic techniques have rapidly increased in recent years. Laparoscopy or pelviscopy require carbon dioxide (CO2) insufflation and Trendelenburg or reverse-Trendelenburg position for operational convenience. Many studies were done about the effects of laparoscopic procedures. But simultaneous comparisons of end-tidal CO2 tension (PETCO2), peak airway pressure (Ppeak), plateau pressure (Pplat) and respiratory compliance (Cdyn), between Trendelenburg and reverse-Trendelenburg position are rare. We compared the airway pressure and compliance between the two positions during laparoscopic surgery. METHOD: Eighty patients were divided into 2 groups: for 10o reverse-Trendelenburg position (n=40, Group R) and 10o Trendelenburg position (n=40, Group T). Abdominal pressure was maintained at 10 mmHg by a CO2 insufflator, and minute ventilation was controlled with a constant tidal volume and fixed respiratory rate. We observed the change of PETCO2, Ppeak, Pplat, and Cdyn at 1 minutes before CO2 insufflation (control value), 2 min after position change, 5, 20, 30, 60 minutes after CO2 insufflation, 2 min after CO2 removal, and 2 min after operation. RESULT: PETCO2, Ppeak, and Pplat were increased and Cdyn was decreased significantly after pneumoperitoneum compared with the control in group R. PETCO2, Ppeak, and Pplat were increased significantly under the Trendelenburg compared with the reverse-Trendelenburg, and Cdyn was decreased significantly in Trendelenburg compared with reverse-Trendelenburg. CONCLUSION: PETCO2, Ppeak, Pplat, and Cdyn impedances increased more under the Trendelenburg after pneumoperitoneum compared with reverse-Trendelenburg. We should pay more attention to patient with pulmonary disease, obesity, and old age under the Trendelenburg than reverse-Trendelenburg position.