Regional cerebral oximetry (RCO), introduced to clinical practice 15 years ago, is a non-invasive method of measuring regional cerebral venous oxygen saturation using optical spectroscopy. Monitoring during anaesthesia is mainly directed at providing optimal oxygenation and avoiding desaturation incidents. RCO offers new and broader possibilities for measurement of cerebral and regional tissue oxygenation.This method has proven useful both in anaesthesia and in intensive care; The article shows the indications for which this method of monitoring may be useful during anaesthesia and in intensive care units, allowing the avoidance of more invasive methods, e.g., mixed venous saturation and venous bulbar saturation. It is also extremely useful in small children in whom cannulation of large vessels may be difficult or impossible. In the review, possible applications of the method are presented and discussed.