In a retrospective study, an evaluation was made of the intra-operative EEG findings and clinical results of 100 consecutive carotid endarterectomies carried out in 90 patients over the period 1977 to 1983. There was no operation-associated mortality; the peri-operative morbidity was 5%. All operations were performed maintaining the systemic blood pressure some 20% above the patients normal value. No interval shunt was used. The surgical policy was not influenced by EEG findings in any of the procedures. There was no relationship between carotid-clamping time and intra-operative EEG changes, nor was there a relationship between EEG changes and clinical outcome. It is most likely that neurological deficit following carotid endarterectomy, if operation is performed during elevated systemic blood pressure, is not due to haemodynamic disturbances, as a consequence of critical reduction of cerebral blood flow during internal carotid artery clamping, but to micro-embolism. From this assumption, it can be concluded that peri-operative complications of carotid endarterectomy cannot be reduced by intra-operative EEG monitoring.