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The fatigue crack propagation behavior from a pre-crack under cyclictorsion combined with static or cyclic axial loading was predicted on the basis of themaximum tangential stress criterion. The prediction was compared with theexperimental results obtained for thin-walled tubular specimens made of a mediumcarbon steel. The direction of fatigue crack propagation follows the direction of themaximum of the total range of the tangential stress, Δσθ max, near the crack tip and thengradually changes to the direction perpendicular to the maximum of the total range ofthe principal nominal stress. The mode II stress intensity factor range quickly gets closeto zero after a small amount of crack extension. The propagation rate was faster thanthe uniaxial data as cracks extended a long distance.