In the frame of studying II–VI oxides of interest in optoelectronic technologies, the structural properties of CdO films grown by metalorganic vapour phase epitaxy on a-plane sapphire substrates have been analysed. The study has been performed by means of X-ray diffraction and cross-sectional transmission electron microscopy measurements. CdO films have been found to grow along [111] with the presence of twinned domains. Asymmetrical reflections have been used to study the crystalline quality of the twinned domains, independent of each other, as well as to determine their relative population. The analysis has been made as a function of growth conditions: VI/II precursors molar ratio and growth temperature.