The paper includes the results of experimental investigations and numerical analysis performed with the aim of studying contact fatigue damage in carburized and shot-peened gearwheels used in gearpumps. On the basis of SEM observations, a model for the evolution of the damage was developed, supposing that the residual stresses induced by shot-peening are mainly effective in stopping microcrack propagation but not in preventing microcrack initiation. In the light of this hypothesis, and following experimental measurements of residual stress, an approach is proposed to evaluate the effect of shot-peening parameters on the performance. The development of this approach required the execution of a numerical analysis of the engagement cycle taking into account the presence of residual stress and microcracks: the results allow one to determine, at least in comparative terms, the parameters that give the best strength improvement against contact fatigue.