The fatigue fracture surface of a duplex stainless steel was analyzed using x- ray fractography. A lower than average austenite content was observed at the fracture surface due to the transformation of austenite into deformation- induced martensite. The influence of fatigue cycling on the transformation was confined to a depth of about 30 μm below the fracture surface. X- ray analyses of both the ferrite- martensite and the austenite phases indicated residual stresses (σr) increasing with depth from the fracture surface and reaching a maximum some tens of microns below the fracture surface. The lower σr observed at the fracture surface has been attributed to the stress relaxation effects caused by the new fracture surfaces created in the crack growth process. The observed decrease in full width at half maximum (FWHM) in the ferrite- martensite phase was presumed to be due to the dynamic recovery effect that was likely to occur within the material close to the crack tip as a consequence of fatigue cycling.