Epitaxial thin films of yttria stabilized zirconia (YSZ) have been grown onto (1120) cut sapphire (Al2O3) substrates by solgel processing. The high crystallographic dissimilarity between YSZ and sapphire causes extremely high strains to build up at the interface. The microstructure of the samples has been investigated by high resolution X-ray diffraction using both a laboratory set-up and synchrotron radiation (ESRF, Grenoble). The strain profile across the film thickness has been recovered using a newly developed method that avoids assumptions regarding the shape of the strain profile. (C) 2003 Elsevier B.V. All rights reserved.