A three-dimensional, electrochemical-transport coupled model is applied to a 50 cm(2) proton exchange membrane (PEM) fuel cell and validated against the current distribution data experimentally measured earlier. A parallel computational methodology is employed to substantially reduce the computational time and make large-scale calculations involving millions of grid points possible. Simulation results are analyzed and validated against the available experimental data of current distribution under fully humidified conditions for two cathode stoichiometry ratios. The comparisons of simulations and experiments point out a lack of agreement in the current distribution, although the average polarization curves are matched nearly perfectly. The numerical simulations correctly capture the comma-shaped local polarization curves observed in the current distribution experiments. (C) 2004 The Electrochemical Society.