A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether the use of cerebral regional oxygen saturation (rSO(2)) monitoring during cardiac surgery can lead to improved clinical outcomes. Altogether 488 papers were found using the reported search, of which eight presented the best evidence to answer the clinical question. The author, year, journal, country of study, study type, patient group studied, relevant outcomes, results and study weaknesses were tabulated. Four prospective and another four retrospective studies involving adult and paediatric patients undergoing various cardiac surgical procedures were selected. These have demonstrated that prolonged intra-operative cerebral desaturations are associated with adverse neurological outcomes and prolonged hospital stay. Further, interventions carried out by thoughtful use of the cerebral oximeter are associated with significant reduction in neurologic injury, major organ morbidity and mortality (MOMM) and duration of hospital stay. Some studies have indicated decreased ventilation and intensive care unit (ICU) stay times as well. Clinical benefit and the lack of use-associated risk of injury at a modest expense support the use of this device routinely in patients undergoing cardiac surgery.