Tools for cold forging, which are often manufactured of high performance powder metallurgically produced (PM) tool steels, fail in many cases due to fatigue. The role of the individual parts of the fatigue failure, fatigue crack initiation, fatigue crack growth and final fracture, in reference to the tool life time is little known. Therefore the fatigue crack initiation and fatigue crack growth behaviour of three tool steels with different microstructure were tested under different parameters. A special technique was developed in order to characterize the fatigue crack initiation in the scanning electron microscope (SEM) under loading conditions which are typical of cold forging dies. The fatigue crack growth behaviour for positive and negative stress ratios was studied on the basis of fatigue crack growth curves. The different fracture mechanisms which occur in the investigated tool steels were characterized by fractographs and overload experiments. On the one hand the investigations served for a better understanding of the fatigue behaviour in these steels and on the other hand to generate methods for a physically based estimation of the lifetime of fatigue loaded cold forging tools.