Molecular dynamics (MD) simulations, performed with embedded atom potentials, are used to understand the formation of defects following displacement cascades in Ni. Different empirical potentials, presenting large differences in stacking fault energy (SFE), are used. Simulations were conducted with primary knock-on (PKA) atom energies of 5-40 keV at a temperature of 10 K. Defects include, depending on the potential, individual point defects (vacancies and interstitials), dislocation loops and stacking fault tetrahedra (SFT). The results are related to TEM observations, and the mismatch between these two pictures is discussed. It appears that in a collision cascade, the formation of an SIFT does not depend only on the SFE but also on other parameters such as the mobility of vacancies and self-interstitials, or the presence of replacement collision sequences. Based on these calculations we suggest that the formation of clusters of vacancies is a prerequisite to the formation of SFTs. (c) 2007 Elsevier B.V. All rights reserved.