The governing equations are formulated for general (axisymmetric or unsymmetric) vibrations of thin circular cylindrical shells of composite material and reinforced with axial (stringer) and/or circumferential (ring) stiffeners. The loading is direct axial compression fluctuating about a mean value. Attention is paid to the dynamic stability of such shells. The shells are modeled by use of three different shell theories (Donnell, Morley, and Sanders) and the stiffeners are modeled as being either discrete or smeared.