The determination of cerebral oxygen saturation (S(c)O(2)) by means of near-infrared spectroscopy allows non-invasive assessment of the cerebral oxygen delivery and demand ratio in the frontal cortex region. Studies in cardiac as well as non-cardiac patients have shown that maintaining S(c)O(2) in the preoperative range reduces the incidence of postoperative cognitive dysfunction and general morbidity; however, S(c)O(2) is not only reflective of cerebral but also of systemic oxygen balance, is inversely related to cardiopulmonary function and has prognostic relevance in cardiac surgery patients. This suggests that cerebral oximetry is not only useful for neurological but also for hemodynamic monitoring and preoperative risk stratification of cardiac surgery patients.