Samples of poly(p-phenylene sulfide) obtained by different thermal and/or mechanical treatments are found to exhibit the same crystal structure. Conformational and packing analysis performed by molecular mechanics have given the lowest energy conformation of the polymer chain in the crystal state and the lowest energy crystal structure. The intensities of the observed reflections measured by a powder diffraction profile have been compared with the calculated intensities for different models of chain conformations and crystal structures. The lowest discrepancy index between calculated and observed intensities is obtained for a structure in very good agreement with that postulated by molecular mechanics.