Finite element methods are used to evaluate all possible fracture modes at the tip of a circumferential crack in an isotropic cylindrical shell subjected to torsion. The finite element results are compared with shallow-shell theory data for cylinders with different geometries. The results indicate that there is good agreement between the membrane stress intensity factors calculated from finite element displacements at the crack tip and the factors found using shallow-shell theory for small crack lengths. For longer cracks, disagreement between these two approaches is very pronounced. In particular, the bending stress intensity factors from the finite element analysis are significantly greater than the corresponding values determined from the shallow-shell theory. It is observed that the out-of-plane, antisymmetric deformation near the crack produces mixed mode fracture with crack opening and tearing displacements.