The dynamic behaviour of a rotor consisting of multidiscs on a solid or hollow shaft, as used in gas or steam turbines, is considered. The effect ofshaft flexibility on the dynamic characteristics of the discs and the coupling ettects between the shaft and disc modes are investigated. The influence of the disc flexibility on the behaviour of the shaft system is also investigated. A new, thick, three-dimensional, cylindrical element is developed for the dYnamic analysis and applied to various geometry of the discs-shaft system. Advantage is fully taken in the analysis of the rotational periodicity of the wave propagation. Results presented for various cases with difering flexibility and geometry show clearly the coupling effects in a multi disc-shaft system. Inference diagrams are developed, from which the dynamic behaviour of a system can be predicted for differing flexibility relationships between the solid or hollow shafts and the discs. The effect of various fixing conditions and boundary conditions on the coupling characteristics are also presented. The theoretical results show very close agreement with the experimental results.