A diffraction profile is here derived from classical Molecular Dynamics (MD) simulation for the hydrated perfluorosulphonic acid fuel-cell membrane material Nafion at 363 K using a 76 angstrom x 76 angstrom x 76 angstrom box. The MD simulation reproduces the phase-separated nanoscale structure of Nafion and water channels. No specific structural features, such as a characteristic channel diameter, could be distinguished. Nevertheless, the envelope of the simulated diffraction profile based on 6000 MD "snapshots" reproduced well the key features of the experimental SAXS profile. This draws into questions previous interpretations of diffraction data for the Nafion (R) system which involve simplistic notions of channel- and cluster-diameter. (C) 2009 Elsevier B.V. All rights reserved.