Natural frequencies of stiffened cylindrical shells are investigated for short and long shells with clamped-clamped boundary condition. The semi-analytical finite element methods is used for the analysis. A cylindrical shell element with four degrees of freedom per node and two nodes per element is used. The stiffness and inertia matrices for the vibrating array of stringers has been obtained from the stiffness and inertia matrices of a single stringer and added to the stiffness and inertia matrices of the shell. The frequencies obtained by this method is compared with existing experimental and theoretical results and found to give reasonable accuracy. The effects of number of stringers and ring stiffeners on the natural frequencies of the shell are investigated. © 1997 Elsevier Science Ltd.