The vibrations of elastic circular cylinders are thoroughly examined by using, for the first time, the “best” first-order shell theory of Sanders. For variations in the wave numbers and the thickness ratio, the effects upon the vibration frequencies, modal amplitude ratio and strain energy are extensively detailed. In addition, comparisons with frequencies calculated from the Donnell, Flügge, and Timoshenko shell theories are given. Also examined in great detail are the various reductions that are obtained from the complete shell theory: e.g., the axisymmetric breathing, torsional and longitudinal vibration modes, beam and plate modes, and the extensional and inextensional ring frequencies. Finally, some comparisons are made between alternative approximations to the radial frequency.