The crystallographic structure of crystalline poly(phenylene sulphide) has been calculated from wide-angle X-ray diffraction pattern of a range of materials with different degrees of crystallinity. The orthorhombic unit cell has parameters refined by a least-squares method: a = 0.868 +/- 0.002 nm, b = 0.566 +/- 0.002 nm, and c = 1.026 +/- 0.005 nm. The crystalline density was determined to be 1.43 g cm(-3) and the enthalpy of fusion of crystalline PPS, DeltaH(f)(0), 76.5 J g(-1) at the mp. Using computer modelling and potential energy minimisation, the torsional angle of the C-S-C bond was determined to be 108 degrees and the phenylene groups arranged at 45 degrees to the plane of the molecular chain. These results have been confirmed by comparison of computed and measured X-ray diffraction intensities.