The flat foot is a very frequent cause of consultation in podology. The lesion is rapidly fixed, and osteoarthrosis appears. The diagnosis is clinical. A podoscopic and radiographic examination is necessary to appreciate the evolutivity of the deformity. The treatment is almost conservative: the wearing of orthesis is often sufficient. The indications of the surgery are rare; sometimes it is possible to do plastic techniques (in particular on the posterior tibial tendon) but, when the foot is painful, the osteoarthrosis is present and it is necessary to do arthrodesis, in particular in the talonavicular joint.