The aim of this work is to investigate the performance of Molten Carbonate Fuel Cells (MCFCs), with external reforming and Gas Turbine/Steam Turbine (GT/ST) combined cycles. The analysis of these MCFC-GT/ST combined cycles has been carried out using the Thermo Economic Modular Program TEMP (Agazzani and Massardo, 1997) modified to allow MCFC, external sensible heat reformer, and catalytic burner performance to be carefully taken into account. The code has been verified through the use of a detailed MCFC model (Bosio et al., 1999) and of the data available for an existing MCFC unit. The thermodynamic and exergy analysis of a number of MCFC combined cycles is presented and discussed, taking into account the influence of technological constraints, also evaluated with the sophisticated model, and the influence of the post-combustion of the fuel directly in the external catalytic burner. The results are presented and discussed in depth.