The dynamic behavior of a geared rotor bearing systems with coupled torsional-lateral motion is investigated using a Hybrid Method which combines the merits of the Finite Element Method and the Generalized Polynomial Expansion Method. The effects of the stiffness and damping of the bearings and the gear mesh, the mesh angle and the location of the gear mesh are also studied. Natural whirl speed analyses and steady state responses due to mass unbalance and transmission error excitation are presented. The accuracy and the efficiency of the method are demonstrated. The results show that the torsional-lateral coupled modes of the system are strongly affected by the stiffness, damping, and mesh angle of the gear mesh. The steady state response amplitudes due to transmission error at tooth passing frequency are high. The application of hybrid method to the geared rotor-bearing system leads to improved computational efficiency compared to the finite element method without lose of accuracy.© 1994 ASME