A two-dimensional, nonisothermal, transient model is developed which is capable of predicting polymer-electrolyte fuel-cell performance during cold start. The accumulation of ice and the transport of water in gas, liquid, and membrane phases at temperatures both above and below 0 degrees C are included. In the porous media, the saturation levels of ice and liquid, as well as their pressures, are predicted based on the physical and chemical properties of the cell materials. Simulation results show that liquid-water transport near but below 0 degrees C plays an important role in determining the cell potential as a function of time during startup because it can allow for rapid drainage of the cathode catalyst layer once enough fine-pore ice has melted. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3592430] All rights reserved.