The growth morphology of NiO and MgO films deposited in the temperature range 300-350 K has been studied by Spot Profile Analysis of Low Energy Electron Diffraction (SPA-LEED) patterns. The oxide films grow layer-by-layer. They are pseudomorphic during the initial stages. Relaxation via the injection of misfit dislocations with {110} glide planes occurs for coverages larger than a critical coverage (Theta (c) approximate to 5 ML for NiO, Theta (c) = 1-2 ML for MgO). The relaxation process leads to the formation of mosaics on the film surface. The tilt angle of the mosaics decreases with increasing oxide thickness due to minimisation of the deformation energy.