A new multiaxial fatigue testing facility is described. It can strain a thin-walled tubular specimen in three independently controlled loading modes by the use of torsion, axial load, and internal and external pressure. Any stress state having a principal stress ratio between equibiaxial (λ = +1) and torsion (λ = −1) with any orientation of the maximum principal stress and the specimen axis can be chosen, with a maximum principal stress of 700 MN/m². The significance of specimen geometry is examined in relation to multiaxial fatigue testing and the design of a suitable specimen is discussed. Test data for a 1 Cr-Mo-V steel are presented to show the variation in multiaxial fatigue results for similar stress states obtained using different test systems and specimen geometries. The possibility of undertaking wider investigation of the effects of anisotrophy and cumulative damage is discussed.