A part to be shot peened includes at least one thin wall (12″) defining two opposite main faces, the square root of the area of each face being greater than the mean distance between the two faces by a factor of at least five, and preferably by a factor of at least ten. According to the method, the part is caused to rotate at least intermittently relative to one or more vibrating surfaces, with at least one of the main faces being exposed to projectiles (6) set into motion by one or more of the vibrating surfaces, treatment taking place progressively on the face(s) so as to impart compression stresses thereto, with a portion only of the part being treated at any one time and with regions of the part preferably being exposed on several occasions to the projectiles, with relative rotation taking place between the exposures.