An implantable prosthesis for repairing a hernia defect in an inguinal region of a human body delimited by the anterior abdominal wall, the psoas muscle and a medial inferior area of the inguinal anatomy, the prosthesis comprising: a piece of biocompatible material having a preformed three-dimensional shape, the piece having a lateral side and a medial side located in opposite directions on a medial-lateral axis and a superior side and an inferior side located in opposite directions on a superior-inferior axis, the inferior direction corresponding to a direction toward feet of a body when the implantable prosthesis is implanted in the body, the piece including: - a first portion, configured to face the anterior abdominal wall, said first portion forming a partial spherical cap surface shaped and dimensioned so as to substantially conform to the shape of the anterior abdominal wall, said first portion having an inferior edge extending along a wavy line from the lateral side to substantially the medial side and defining a medial inferior corner of the first portion, - a second portion, configured to face the psoas muscle, said second portion extending from the inferior edge of said first portion and forming a wavy-shaped wall extending from the lateral side to substantially the medial side of the piece, shaped and dimensioned so as to substantially conform to the shape of the psoas muscle, - a third portion forming an arched part, said arched part extending longitudinally substantially in the inferior direction from a medial part of the inferior edge of said first portion including said medial inferior corner of said first portion, said arched part extending radially substantially in the front direction, said arched part being shaped so as to cover the organs present in the inferior area of the inguinal region, said third portion being configured to face the medial inferior area of the inguinal anatomy. a piece of biocompatible material having a preformed three-dimensional shape, the piece having a lateral side and a medial side located in opposite directions on a medial-lateral axis and a superior side and an inferior side located in opposite directions on a superior-inferior axis, the inferior direction corresponding to a direction toward feet of a body when the implantable prosthesis is implanted in the body, the piece including: - a first portion, configured to face the anterior abdominal wall, said first portion forming a partial spherical cap surface shaped and dimensioned so as to substantially conform to the shape of the anterior abdominal wall, said first portion having an inferior edge extending along a wavy line from the lateral side to substantially the medial side and defining a medial inferior corner of the first portion, - a second portion, configured to face the psoas muscle, said second portion extending from the inferior edge of said first portion and forming a wavy-shaped wall extending from the lateral side to substantially the medial side of the piece, shaped and dimensioned so as to substantially conform to the shape of the psoas muscle, - a third portion forming an arched part, said arched part extending longitudinally substantially in the inferior direction from a medial part of the inferior edge of said first portion including said medial inferior corner of said first portion, said arched part extending radially substantially in the front direction, said arched part being shaped so as to cover the organs present in the inferior area of the inguinal region, said third portion being configured to face the medial inferior area of the inguinal anatomy. - a first portion, configured to face the anterior abdominal wall, said first portion forming a partial spherical cap surface shaped and dimensioned so as to substantially conform to the shape of the anterior abdominal wall, said first portion having an inferior edge extending along a wavy line from the lateral side to substantially the medial side and defining a medial inferior corner of the first portion, - a second portion, configured to face the psoas muscle, said second portion extending from the inferior edge of said first portion and forming a wavy-shaped wall extending from the lateral side to substantially the medial side of the piece, shaped and dimensioned so as to substantially conform to the shape of the psoas muscle, - a third portion forming an arched part, said arched part extending longitudinally substantially in the inferior direction from a medial part of the inferior edge of said first portion including said medial inferior corner of said first portion, said arched part extending radially substantially in the front direction, said arched part being shaped so as to cover the organs present in the inferior area of the inguinal region, said third portion being configured to face the medial inferior area of the inguinal anatomy.