Formulations are presented for the rotordynamic analysis of a composite rotor supported on general, eight coefficient bearings, obtained by using conventional equivalent modulus beam theory (EMBT), and a layerwise beam theory (LBT) derived from an existing layerwise shell theory, respectively. The formulations are based on the principle of virtual work. Rayleigh-Ritz displacements are used for deriving the solution equations. The results indicate that the difference between the two theories is not large, but for unsymmetric stacking sequences with bending stretching couplings present, the EMBT may result in inaccurate predictions of rotordynamic behavior. Furthermore the layerwise theory produces a more realistic stress field in the laminate. © 1996 Academic Press Limited.