Internally humidified, edge-air-cooled PEFC stacks are promising for portable systems in terms of specific power and specific cost. However, their main drawbacks are thermal power limitations due to limited heat removal from inside the stack. The aim of this work is to minimize the cooling limitation with a simultaneous cost and weight reduction by optimization of the stack geometry. A steady-state, thermal FE-model was developed and validated against experimental temperature distributions. The model includes anisotropic heat conduction and heat convection by the cooling air. Cell voltage, liquid water fraction and limiting temperature were experimentally determined for improved accuracy. Complex flowfield structures were approximated with the numerical volume averaging method to reduce computational cost. As a result of the optimization study specific power was improved by +86% with simultaneous reduction of specific cost by -35%. (C) 2007 Elsevier B.V. All rights reserved.