Yttria-stabilized zirconia (YSZ) thin films were prepared on thermally oxidized Si-wafer substrates using ion-beam assisted laser deposition (IBALD). Biaxially oriented crystal growth with the [001]-axis parallel to the substrate normal and the [111]-axis parallel to the impinging argon ion beam was obtained for a range of deposition parameters. The film growth and crystallite orientation were observed in situ by reflection high-energy electron diffraction (RHEED). During film deposition, the crystal structure and crystallite orientation were monitored in the diffraction pattern. The in-plane orientation of the grown film surface was determined quantitatively by evaluating changes in intensity of selected spots in diffraction patterns recorded while rotating the sample around the substrate normal. The obtained intensity distribution is a convolution of crystallite orientation and beam broadening effects due to crystal strains and crystallite dimensions. The effects of limited crystal size and mosaic spread are evaluated from a recorded diffraction pattern and deconvoluted from the spot intensity distribution over the rotation angle, giving the crystallite in-plane alignment. The results are in good agreement with X-ray diffraction. A possible explanation for the improved in-plane alignment of YBa2Cu3O7-delta films compared with the YSZ buffer layers is given. The grown films were analysed ex situ by X-ray diffraction for crystal analysis and by atomic force microscopy for characterization of the surface roughness and crystallite size. Film strains were related to argon implantation into the films during deposition.