Drop tests of different types of helmets were performed with different drop velocities and points of impact on the helmet. A close relation showed between HIC and peak acceleration. An investigation of experimental and theoretical acceleration vs. time curves indicated that the shock absorption performance of current helmets is more affected by the thickness of the protective padding than by its energy absorption capacity. The influence of rotational acceleration on the headform was under investigation as well. It was demonstrated that rotational acceleration can be nearly 5 krad/s2 in normal test conditions as specified in ECE-R 22.