A simple 1-dimensional Monte Carlo (MC) model has been developed to simulate the chemical vapour deposition (CVD) of a diamond (100) surface. The model considers adsorption, etching/desorption, lattice incorporation, and surface migration along and across the dimer rows. The reaction probabilities are taken from experimental or theoretical literature values for standard CVD diamond conditions. Renucleation events believed to be due to reactive adsorbates, such as C atoms or CN groups, were modelled by creating random surface defects which form a critical nucleus upon which to nucleate a new layer. By assuming that migrating C species that encounter these surface defects add to the growing surface by templating either from the underlying layer or from the surface defect, and with suitable colour coding, the evolution of different grains has been modelled. On increasing the probability of creating surface defects, the number of grains increases while their mean size decreases. This simulates the film morphology changing from that of single crystal diamond to microcrystalline, nanocrystalline and finally ultrananocrystalline diamond. With the formation of such defects which can act as renucleation points turned off, but using random seed crystals, the films develop a columnar structure similar to that observed for heteroepitaxial microcrystalline diamond. (C) 2009 Elsevier B.V. All rights reserved.