The vibration in rotating machinery is mostly caused by unbalance, misalignment, mechanical looseness, shaft crack, and other malfunctions. The diagnostics of rotor faults have been gaining importance in recent years. Many papers in the literature have dealt with single fault identification, but, normally, more than one fault can occur in a rotor. In the present study a model-based method is proposed for the on-line identification of faults in a rotor. The fault-induced change of the rotor system is taken into account by equivalent loads in the mathematical model. The equivalent loads are virtual forces and moments acting on the linear undamaged system to generate a dynamic behavior identical to that measured in the damaged system. The rotor has been modeled using the finite element method with unbalance and crack as the considered faults. Different shape expansion methods are compared for fault identification. The identification process is also simulated when both unbalance and crack are acting simultaneously on the rotor. The fault size and location have been identified while the nature and symptoms of the faults are ascertained using fast Fourier transform. © 2005 Sage Publications.