Knowledge-based molecular modelling, crystal packing calculations and diffraction-simulation techniques are combined with existing X-ray powder and fibre diffraction data to investigate the crystal and molecular structure of poly(1,4-phenylenesulfone). The unit cell thus obtained has C-centred orthorhombic symmetry (two chains per cell), space group Cmcm, with dimensions a = 10.79, b = 5.05, c = 9.97 Angstrom and density 1.71 g cm(-3). The polymer chain adopts 2(1) helical geometry, with aromatic ring planes orthogonal to a plane defined by the bridging C-S-C groups. Crystal packing is dominated by S=O...H-C van der Waals’ contacts (O...H = 2.68 Angstrom). The final model is consistent with X-ray data for poly(1,4-phenylenesulfone) produced not only by self-polycondensation of [1,4-FC6H4SO2](-), but also by peroxide oxidation of poly(1,4-phenylenesulfide).