Background: The goal of the study was to investigate the combined effect of the steep(15°-20°). Trendelenburg position and CO2 pneumoperitoneum on cardiovascular, and respiratory homeostasis during ovarian cyst laparoscopy. Methods: In this prostective study. 216 consecutive patients in Tu Du hopital who underwent ovarian cyst laparoscopy under general anaesthesia. Heart rate, mean arterial pressure, SpO2, PetCO2 , Pplat, tidal volume, and minute ventilation were monitored and recorded. Results: Although patients were in the Trendelenburg (15°-20°) position, all variables investigated remained within a clinically acceptable range. PetCO2 increased from 28,46 + or - 2,88mmHg to 36,13 + or - 3,1mmHg (P0.05) and respiratory plateau pressure(Pplat) gradually increased from 14(5)cm H2O to 26(8)cm H2O (P0,05) after applying CO2 peritoneum during Trendelenburg positioning. Conclusions: Combination of the steep Trendelenburg (15°-20°) position and CO2 pneumoperitoneum was well tolerated. Haemodynamic and respiratory variables remained within safe limits in ovarian cyst laparoscopy.