The mechanical behavior of Co-20Cr-15W-10Ni alloy is studied by compression tests at high temperature. Microstructures after deformation are evaluated using SEM-EBSD. Significant grain refinement occurs by dynamic recrystallization for high temperatures and low strain rates [T > 1373 K (1100 A degrees C), strain rate < 0.1 s(-1)], and at high strain rates (strain rate similar to 10 s(-1)). Dynamic recrystallization is discontinuous and occurs by nucleation of grain boundaries, leading to a necklace-like structure. The nucleation mechanism is most likely bulging of grain boundaries. However, recrystallization occurs also by rotation of annealing twins, which can bulge as well. Modeling of the observed mechanical behavior gives a fair quantification of flow softening due to dynamic recrystallization, indicating the progress of dynamic recrystallization with deformation.