Wide-angle X-ray scattering (WAXS) patterns of isotactic polypropylene (iPP) were analyzed in terms of the ideal WAXS patterns of their individual phases. Analysis was done with the technique of simulated annealing. This analysis is a novel method for simultaneously obtaining the volume fractions of the crystalline and amorphous phases and the average lamellar thickness of the individual crystalline phases. The method is different from traditional methods as it allowed us to obtain a large amount of information in a single step from a single WAXS pattern. This study was limited to a few selected specimens of iPP, but the method expounded could, in principle, be extended to other polymers and polymer blends. The limits of its applicability and possible shortcomings are discussed. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2386-2394, 2010