During gynaecological laparoscopic surgery, alterations in cerebral blood flow and intracranial pressure are frequently reported. These changes affect cerebral perfusion pressure and thus may affect cerebral oxygenation. In this prospective study, the effect of gynaecological laparoscopic surgery on cerebral oxygenation was examined by following the changes in regional cerebral oxygen saturation (rSO 2 ). Twenty-four female patients were enrolled. The mean rSO 2 was 65.5 ± 5.4% at baseline before surgery, 60.8 ± 5.6% when the patient was placed in the Trendelenburg position, 57.1 ± 9.3% after creation of pneumoperitoneum, and 64.0 ± 7.3% after the completion of surgery. During the period of pneumoperitoneum, rSO 2 fell below 50% in two hypercapnic patients. In comparison with baseline, rSO 2 declined significantly in the Trendelenburg position. The creation of pneumoperitoneum itself did not decrease the average rSO 2 value further unless the patients were hypercapnic.