The results of kinetic Monte Carlo simulations of a realistic model of postdeposition island growth that takes into account the spatial extent of islands are presented. Simulations were carried out on oneand twodimensional substrates for different values of the critical island size i and were compared with previous results for a point-island model. The use of a realistic island geometry results in enhanced island aggregation and coalescence. This leads to an increase in the average island size S as well as the exponent z describing the dependence of S on coverage. The shape of the island-size distribution for i53 also changes dramatically due to the existence of ‘‘magic’’ islands.