Rubber-modified polyamides were probed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering and various mechanical tests. TEM studies showed that in tough samples the crystalline orientation in the interparticle region is of a distinctly different character. The lamellae are organized perpendicular to the rubber-matrix interface, while the hydrogen-bonded planes of low slip resistance are aligned parallel to these interfaces. Based on this observation a model is proposed to elucidate the deformation and toughening mechanisms of these materials. Further SEM studies in the stress-whitened regions of both the tensile bars and Izod specimens revealed the evolution of a cavitation process in the rubber particles. The shape and the size of the cavities in tough samples is related to the initial morphology of the matrix.