Surface hardening is used in the aerospace industry to increase the fatigue life of critical structural com-ponents. Processes such as induction hardening are gradually replacing traditional non-environmentalfriendly surface treatments. Modern induction generators allow simultaneous heating with medium and high frequencies. A large range of process parameters are then available and may be varied to obtain a given hardened depth but with different residual stress distributions. In this paper, residual stress andmicrohardness gradients are measured in spur gears after four different types of induction surface treat-ment. An accurate methodology is proposed to measure and correct XRD results for layer removal andX-ray elastic constant variations from case to core. The results indicate that induction parameters havea significant effect on the residual stresses and that the best type of treatment could be contour harden-ing with a significant preheating and a final dual-frequency heating. The propose methodology could beadapted for measurements in other complex parts presenting deep microstructural and residual stressgradients.Measurement and correction of residual stress gradients inaeronautical gears after various induction surface hardening treatments