Numerical simulations of a proton exchange membrane fuel cell were carried out for various temperatures ranging from well below the freezing temperature of water to a moderate ambient temperature, and also for various inlet temperatures, to investigate its performance. A three-dimensional serpentine flow field was used to determine the cell behavior temperature conditions. The saturation of liquid water was considered for various ambient temperatures in order to obtain realistic estimates of cell performance, with special emphasis placed on sub-cooled temperatures. Results show that both the ambient and the inlet temperature have strong influences on cell performance, although the inlet temperature has much more important influence than the ambient temperature. In addition, liquid water saturation is enhanced at higher inlet temperatures. Moreover, for sub-cooled ambient temperatures the liquid saturation level is higher in the shoulder region near the inlet section than in the outlet section; this trend is reversed for higher ambient temperatures. There is a high probability that operation of the cell at sub-cooled temperatures and higher inlet temperatures will result in the formation of ice throughout the system, which may further degrade the cell performance. The model was validated by comparison of predicted polarization curves with those found in the literature. Copyright (C) 2010 John Wiley & Sons, Ltd.