The problem of parametric vibrations of long circular cylindrical shells prestressed by a uniformly distributed transverse static load has been considered. The static equilibrium position is found as a result of the solution of a nonlinear problem, where the factors contributing to nonlinearity include flattening of circular cross sections during deformation, stretching of elastic axis and hardening elastic foundation. Small amplitude forced parametric vibrations about the static position are then studied. The solution of the nonlinear parametric vibration problem in the absence of the static load is also shown. © 1988.