This article describes the incorporation of a population balance model (PBM) based on the classes method into the commercial CFD-code STAR-CD. The numerical approach of the PBM solution was initially validated with experimental data on the agglomeration of polystyrene particles in a shear flow. The PBM was then incorporated into STAR-CD with the use of the "generic scalars" provision in that software, coding the source terms with "user subroutines." The resulting CFD-PBM model was validated for a second time and further verified on several standard flow geometries. This paper complements earlier works of other authors who applied the method of classes to similar PBM-related problems. (C) 2014 Elsevier B.V. All rights reserved.