Residual stresses are one of the crucial parameters determining the performances of structural as well as functional materials. In the case of coatings and films, the substrate and the deposition process may determine very high residual stress fields which can affect both performances and surface integrity, since adhesion or cracking resistance can be strongly altered. The accurate and reliable assessment of residual stress is thus mandatory for the evaluation of these materials. In this paper we applied a new approach to evaluate the residual stress by means of the analysis of a single 2D-diffraction image collected by a laboratory X-ray microdiffractometer equipped with an image plate detector. The residual stress in thin films of LaCoO3 was calculated and correlated to cubic-to-rhombohedral phase transformation. (C) 2003 Elsevier B.V. All rights reserved.