Three-dimensional simulations of grain growth in thin films containing finely dispersed second-phase particles were performed using a phase field model. The simulations show that although the growth behavior of the columnar grain structures in thin films is essentially two-dimensional, the interaction between the particles and the grain boundaries is three-dimensional. Grain boundaries can therefore more easily break free from the particles than in purely two-dimensional systems, resulting in fewer grain boundary-particle intersections and a larger final grain size. For a given volume fraction f(v) and size of the particles r, the final grain size (R) over bar (lim), increases with film thickness. Moreover, it was found that particles located in the middle of the film are most efficient in pinning grain boundaries. A classical Zener type relation <(Rover bar>(lim) /r = K(1/f(v)(b)) cannot describe these effects. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.