Controlled hypotension is one of the techniques applied to several microscopic ear, nose, and throat (ENT) surgeries. However, this technique has risks and complications, which result in impaired perfusion and oxygenation of organs including the brain that could trigger the postoperative cognitive dysfunction (POCD). Damage that occurs in brain cells can trigger the secretion of biomarker proteins in the blood, one of which is S100B which can indicate nerve damage in the intra and postoperative period. This study aimed to analyze the correlation between S100B protein level and the incidence of POCD in patients who received ENT surgeries with controlled hypotension