Background/aim: This study aimed to evaluate the relationship between the Trendelenburg position and cerebral hypoxia in robot-assisted hysterectomy and prostatectomy.Materials and methods: A standardized mini-mental state examination was administered to 50 patients enrolled in the study 1 h before and after surgery. Near infrared spectroscopy (NIRS) values and hemodynamic and respiratory parameters were recorded after induction of anesthesia (baseline) and once every 20 min in the Trendelenburg position and supine positions. The relationship between the development of cerebral desaturation and the patient's position was examined. Results: For all patients, the baseline mean cerebral oxygen saturation (RSO2) on the right and left were 70.5 ± 7.3% and 70.6 ± 6.7%, respectively. Right RSO2 values at 20 min and 60 min in the Trendelenburg position decreased significantly, but they increased at 120 min. A significant positive correlation was found between right RSO2 and EtCO2 in the supine period following surgery, and between left RSO2 and EtCO2 at 60 min in the Trendelenburg and supine positions. The relationship between NIRS values and cognitive dysfunction was not significant.Conclusion: We found that cerebral saturation decreases as age increases, and cerebral desaturation may occur owing to the Trendelenburg position. There was no correlation between patients? cognitive function and NIRS values.