The microstructure of a diamond him largely determines its properties and performance. Several diamond films have been deposited by HFCVD at different methane concentrations and consequently at different growth rates. The evolution of the films microstructure has been analysed by X-ray diffraction and Raman spectroscopy, with specific attention to the 1332 cm(-1) line width. By the X-ray diffraction data the crystallite size distributions have been derived both for the (111) and the (220) reflections. The observations support the view that the microstructure of HFCVD diamond films is determined by a Van der Drift kinetic evolutionary selection principle.