In this paper a generalized model, based on system-level approach, for predicting the High Temperature Fuel Cells (HTFCs) behavior and performance is presented. The system-level model allows to forecast the HTFC performance under different operating conditions (cell temperature, anode off-gas recirculation, reactants temperatures, fuel and oxidant utilization factors, etc.) and cell design (tubular and planar configurations and with co-flow, counter-flow and cross-flow arrangements). Mass and energy balances are solved by considering both the electrochemical (i.e. electro-oxidation of hydrogen) and thermochemical reactions (i.e. reforming and shifting reactions) which occur in the anode and cathode sides and by applying different equations systems to take into account the type of fuel cell (MCFC or SOFC). The ability of the proposed model in the HTFCs performance prediction is pointed out by the model validation carried out by using experimental data and by analyzing the impact of the model calibration parameters on the cell voltage calculation carried out by means of a sensitivity analysis. Numerical results show that the model allows to characterize the behavior of the HTFCs with a good approximation so, thanks to the simplicity of the simulation procedure and to the small computational time efforts, it can be a useful tool for predicting the performance of hybrid power plants or more complex systems in which the fuel cell is one of the main components. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.