Perthes's disease corresponds to an interruption of the vascularization of the epiphyseal nucleus of the femoral head followed by avascular necrosis. This necrosis weakens the bone and subchondral fractures associated with a deformation of the femoral head is seen. It is important not to miss an extrusion of the femoral head, which makes surgical treatment unavoidable. The loss of joint congruence causes functional limitations and represents an increased risk for early hip osteoarthritis. Non weight bearing limits the subchondral fractures, but requires an important adaptation from the patient and his entourage.