OBJECTIVE Carotid endarterectomy (CEA) is an established surgical procedure for the treatment of internal carotid artery stenosis. Stroke is the commonest risk factor during CEA, therefore, cerebral monitoring became essential. Currently the EEG bispectral index (BIS) is used as a monitor of depth of anesthesia and it has showed decreasing trend during cerebral ischemia. We conducted this study to document the changes of the BIS variable during CEA under anesthesia. METHODS Ten patients who underwent CEA under general anesthesia were studied. The EEG BIS was measured during the perioperative period where five phases were identified: (A) before induction of anesthesia, (B) before clamping of ICA, (C) during clamping of ICA, (D) after declamping of ICA and (E) during the recovery from anesthesia. RESULTS The age ranged between 53-69 yr. The mean values of the BIS were 91.4 +/- 5.6, 59.6 +/- 18.7, 44.3 +/- 6.8, 54.7 +/- 8.3 and 72.1 +/- 12.4 during A, B, C, D and E phases respectively with statistical significant low values during B, C, D and E phases versus phase A. CONCLUSIONS The decreasing trend of the EEG BIS was shown during ICA clamping and whether this is an important quantitative variable to determine the adequacy of cerebral perfusion during CEA yet to be further studied.