In spite of its relative operational simplicity and earlier attempts to model its performance, the Vertical shaft impact (VSI) crusher is still lacking a comprehensive mathematical description that allows predicting its performance accurately. One of the reasons is the limited knowledge of particle interaction and solids flow inside the machine. The paper deals with the application of the discrete element method (DEM) in the prediction of solids flow within a pilot-scale VSI crusher operating under different conditions. A large amount of data has been generated and used to calculate the collision energy spectra, as well as the residence time distributions of rock particles that are fed to the machine. It is shown that the collision energy distribution and frequency change significantly if rock or a ring of steel anvils is used as the target and also if a cascading flow of material bypasses the rotor directly into the crushing chamber. Finally, it is discussed how these data, along with models that describe breakage and damage of single particles, can serve as the basis for the development of a fully-predictive model of comminution in this machine in the future. (C) 2012 Elsevier Ltd. All rights reserved.