Cerebral oximetry is commonly being advocated as a monitor for regional cerebral tissue oxygenation during cardiac surgery. We have increasing concern about the accuracy of this monitor, including the current systems entering the market, with new probes and algorithms. We present 2 cases where cerebral oximetry failed to accurately portray cerebral oxygenation. In the current form, cerebral oximetry may at best be an expensive tool without any benefit on outcomes. In addition, it may contribute to misleading and confusing clinical data.