This paper develops an axi-symmetric approach to dynamic finite element analysis of thin-walled cylinders that permits the inclusion of initial bi-symmetric radial distortion of the cylinder. The motivation behind this development is to allow simplified analysis of thin-walled piles during installation. Initial out-of-roundness of the cross-section of such piles may grow during the installation process. Full three-dimensional dynamic simulation of such problems is prohibitively expensive. This paper takes advantage of the observed bi-symmetric tendency of the cross-sectional distortion of thin-walled piles. A finite element model is developed which uses a Fourier expansion of the displacements in the circumferential direction, while permitting an initial out-of-roundness. The performance of this simplified model is compared with full three-dimensional finite element analysis, and is shown to represent the dynamic behaviour of the distorted cylindrical shell very well. (c) 2005 Elsevier Ltd. All rights reserved.