Near infrared spectroscopy is a relatively new technique for monitoring intracerebral oxygen saturation. Using the technique, three episodes of cerebral hypoxia were detected during elective carotid endarterectomy which were not reliably recorded by more standard monitoring of cerebral perfusion. In one case, cerebral hypoxia was related to slippage of the tracheal tube into the right main bronchus and in the other two to episodes of hypotension. Near infrared spectroscopy is a reliable indicator of peripheral cortical perfusion and provides continuous and noninvasive monitoring of intracerebral oxygen saturation.