BACKGROUNDS: Carbon Dioxide (CO2) insufflation during thoracoscopy may result in adverse hemodynamic consequences such as increase in central venous pressure, decrease in cardiac output and increase in arterial carbon dioxide pressure. But the cerebral effects of CO2 insufflation during thoracoscopy are not known yet. To evaluate the cerebral effect of CO2 insufflation during thoracoscopy, jugular bulb venous blood oxygen saturation and pressure were measured. METHODS: Nine patients were underwent thoracic surgery by thoracoscopy and one lung ventilation. After operation, CO2 was insufflated and hemodynamic parameters, arterial blood pressure, heart rate, central venous pressure, jugular bulb pressure, arterial blood gases and jugular bulb venous blood gases were measured at intrathoracic pressure 5 mmHg, 10 mmHg and 15 mmHg respectively. RESULTS: Central venous pressure was increased with insufflation of CO2 of 10 mmHg and 15 mmHg. Jugular bulb pressure was increased with insufflationof of CO2 of 5mmHg, 10 mmHg and 15 mmHg. Arterial PCO2, jugular bulb venous PO2 and jugular bulb venous blood oxygen saturation were increased with insufflation of CO2 of 5 mmHg, 10 mmHg and 15 mmHg. CONCLUSION: CO2 insufflation pressure of 5 mmHg or greater resulted in significant increase in jugular bulb venous blood oxygen saturation and pressure.