Aim: In this study, we aimed to observe the effect of head position during thyroidectomy on carotid artery blood flow, cerebral oxygen saturation (rSO2) and postoperative cognitive dysfunction (POCD).Material and Methods: Forty patients were included in the study. The time-average velocity (TAV), peak systolic velocity (PSV), end-diastolic velocity (EDV), flow volume (FV), carotid artery diameter (CAD), and resistance index (RI) of the common carotid artery were measured using Doppler ultrasonography when the patient was in supine position before anesthesia, after surgical position (semi fowler position with extension of the neck and head), and before position correction at the end of the surgery. Bilateral rSO2 values were monitored continuously. Cognitive functions were evaluated with the standardized mini-mental test.Results: At the end of the operation, it was determined that FV, PSV, EDV, CAD and bilateral rSO2 values decreased compared to the initial values (p <0.05). Early and late POCD were found to be 47.5% and 32.5%, respectively. No relationship was found between cerebral desaturation and POCD. It was observed that the decrease in FV might be related to early POCD (p <0.05).Discussion: The head position caused a decrease in carotid blood flow, and bilateral rSO2, and these outcomes became more pronounced towards the end of the surgery. Although there was a correlation between early POCD and a decrease in FV, there are many factors that might have affected POCD.