In this paper, a multiphase multidimensional PEM fuel cell model for cold-start simulations has been employed for numerical analyses of the non-isothermal self-start behaviors of a PEM fuel cell from subfreezing startup temperatures, focusing on the coupled phenomena of the ice formation and temperature increase inside the cell. The roles played by many key influential parameters, including the water vapor concentration in the cathode gas channel, the initial water content inside the membrane, the operating current density, and the startup cell temperature, are carefully examined. Numerical results indicate that decreasing the interfacial water vapor concentration at the gas diffusion layer and gas channel surface on the cathode side of the cell would delay ice precipitation and prolong the cell operation time. Decreasing the operation current density and the initial water content inside the membrane, and increasing the startup cell temperature are beneficial for the non-isothermal cold starts of the PEM fuel cell and could lead to successful self-starts. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.