The deformation and damage mechanisms arising during thermomechanical fatigue of a high-Cr single crystal superalloy have been investigated and a completely new failure mechanism involving recrystallization and oxidation has been discovered. The primary deformation mechanism is slip along the {1 1 1} planes. The deformation is highly localized to a number of bands, where recrystallization eventually occurs during the thermomechanical fatigue process. When the final failure occurs along these recrystallized bands it is accompanied by the formation of voids due to the presence of grain boundaries. The damage process is further enhanced by oxidation, since recrystallization occurs more easily in the γ′ depleted zone under the oxide layer.