The thermal conductivity of the polymer electrolyte membrane (PEM) of fuel cells is an important property affecting the overall cell performance. However, very few studies or fuel cell models include the dependence of this property on temperature and humidification conditions. In addition, no detailed studies have been reported for the quantitative understanding of how this property influences important aspects of the cell such as performance, water management, and membrane durability. This work presents results of a sensibility study performed for different membrane thermal conductivities, analyzing the influence of this parameter on the main cell response variables. The work has been performed with the aid of a computational fluid dynamics (CFD) model developed for a 50 cm2 fuel cell with serpentine flow field bipolar plates, previously validated against experimental measurements. The results show to what extent the cell performance, water management, and durability issues such as MEA temperature gradients are influenced by the membrane thermal conductivity, especially at high current densities, leading up to a 50% increase in the cell electric power at 1000 mA/cm2 when the thermal conductivity of the membrane is set to 0.26 W/(m K) instead of to the base value of 0.13 W/(m K).