The present invention relates to a prosthesis for repairing a inguinal hernia defect. The prosthesis includes a piece of biocompatible material having a preformed three-dimensional shape including: a first portion forming a partial spherical cap surface, shaped and dimensioned so as to substantially conform to the shape of the anterior abdominal wall; a second portion extending from an inferior edge of the first portion and forming a wavy-shaped wall, shaped and dimensioned so as to substantially conform to the shape of the psoas muscle; and a third portion forming an arched part extending longitudinally in the inferior direction from a medial inferior corner of the first portion, the arched part extending radially substantially in the front direction, the third portion being intended to face the medial inferior area of the inguinal anatomy.