An impact fatigue test has been designed for studying the repeated biaxial impact load response of polymers. In the test geometry, a thin plate-like sample is rigidly held by an annular clamp and is repeatedly impacted by a hemispherically-tipped plunger. Results have been obtained for polycarbonate. Under impact fatigue, cracks initiate on the bottom surface where high biaxial tensile stresses exist. These cracks propagate along radial lines on the sample surface and also into the sample normal to the surface. The load-bearing capability and the residual impact strength decrease as the cracks propagate. The development of impact fatigue cracks, the lifetime behaviour and the change in mechanical properties after partial impact fatigue are discussed.