The aim of this work is to investigate the performance of internal reforming solid oxide fuel cell (IRSOFC) and gas turbine (GT) combined cycles. To study complex systems involving IRSOFC a mathematical model has been developed that simulates the fuel cell steady-state operation. The model, tested with data available in literature, has been used for a complete IRSOFC parametric analysis taking into account the influence of cell operative pressure, cell and stream temperatures, fuel-oxidant flow rates and composition, etc. The analysis of IRSOFC-GT combined cycles has been carried out by using the ThermoEconomic Modular Program TEMP (Agazzani and Massardo, 1997). The code has been modified to allow IRSOFC, external reformer and flue gas condenser performance to be taken into account. Using as test case the IRSOFC-GT combined plant proposed by Harvey and Richter (1994) the capability of the modified TEMP code has been demonstrated. The thermodynamic analysis of a number of IRSOFC-GT combined cycles is presented and discussed, taking into account the influence of several technological constraints. The results are presented for both atmospheric and pressurized IRSOFC. [S0742-4795(00)00501-9]