The influence of aluminium hydroxide particle morphology and magnesium hydroxide surface coating on the anisotropy and microstructure heterogeneity of injection-moulded discs of polypropylene (PP) filled with 40% by weight of these fillers has been studied through wide-angle X-ray diffraction measures. In general, the discs displayed an anisotropic structure due to different orientations of both filler particles and PP crystals through the part thickness. The samples also exhibited some degree of heterogeneity due to different levels of particle orientations in specimens far away and close to the disc mould entrance.