Torsional buckling of thin cylindrical rotor cans in hermetically sealed motors is typically not considered a likely potential failure mode in conventional motor design applications. However, in unique design applications that have several motors stacked in series, the last rotor may sustain multiple times the torque of a single rotor. Conservative hand calculations indicate rotor can torsional stresses that substantially exceed the torsional buckling capacity of a free-standing cylinder based on Donnell’s thin shell theory. Since the buckling mode shape of a free-standing cylinder includes both radially inward and outward deflections, it is expected that the rotor core will act as internal confinement and thereby increase the allowable torsional stress by suppressing radially inward deflection. A further increase in allowable torsional stress is expected for motor applications involving externally pressurized rotor cans. A complete analytical solution for torsional buckling of a thin cylindrical shell with internal confinement and external pressure was not found in the available technical literature. Therefore, a numerical approach using three-dimensional (3D) finite element analysis (FEA) with a simplified representation of the rotor can and core geometry was undertaken to demonstrate that both internal confinement and external pressure act to significantly increase the rotor can torsional buckling capacity, thereby eliminating torsional buckling as a potential failure mode for the evaluated motor design. The FEA simulations include both linear and nonlinear buckling analysis and utilized 3D quadratic shell elements with surface contact elements at the interface between the rotor can and slotted rotor core. To represent the boundary condition at both welded ends of the rotor assembly, all degrees of freedom were constrained, except in the circumferential direction to allow application of the torque. For the nonlinear buckling simulations, an initial perturbation of the ideal cylindrical geometry is required to initiate buckling and it was conservatively assumed that the initial geometric imperfection aligned with the first mode shape extracted from a linear (eigenvalue) torsional buckling analysis of the free-standing rotor can. Various FEA cases were performed to examine the sensitivity of the rotor can torsional buckling capacity to the assumed initial geometric imperfections (via mode shape perturbation amplitudes or rotor slot hydroformed geometry), external pressure magnitudes, initial radial clearance between rotor can and core, and interface friction coefficient. Elastic material properties at room temperature were assumed for all cases to facilitate relative comparison of results. The FEA results for the rotor can with internal confinement are compared to the free-standing rotor can results to demonstrate the improvement in torsional buckling capacity predicted by nonlinear FEA.