The aim of the study was to evaluate the usefulness of continuous monitoring of regional cerebral oxygen saturation (rSO2) for detection of brain ischemia during carotid endarterectomy.Material and methods. We performed 44 carotid endarterectomies using regional anesthesia, with simultaneous regional cerebral oxygen saturation monitoring in both hemispheres of the brain.Results. Oxygen saturation in the hemisphere ipsilateral to the operated carotid artery dropped from 65.1±8.1 to 58.2±10.7 after carotid artery cross-clamping. The difference was statistically significant (p<0.005). Oxygen saturation in the hemisphere contralateral to the operated artery did not demonstrate a difference between that before or after carotid artery closure (65.7±9.2 and 66.1±10.2, respectively, p=0.1). In five patients (11.4%) carotid artery clamping was associated with the appearance of neurological deficits. Shunt usage was necessary in four cases; the rSO2 decreased by 19.2±14% in this group. In the group without neurological deficit during carotid clamping, the rSO2 decreased by 9.7±10.3% (the difference between groups with and without neurological deficit was not statistically significant, p=0.5). In patients with a rSO2 drop above 20%, the sensitivity of the cerebral oximetry was 20% and specificity 97.5%, while the negative predictive value was 90.7%.Conclusions. Continuous cerebral oximetry is a simple and non-invasive method of patient monitoring during carotid endarterectomy. The rSO2 decreases significantly after the ICA clamping. The sensitivity of cerebral oximetry in prediction of neurological deficit during the procedure is low. Defining the threshold value of rSO2 decrease after ICA clamping as an indication for shunt was not possible with the results of this study.