Overgrowth of the lower jaw that is often associated with underdevelopment of the upper jaw or even the entire midface and a crossbite (inverted overbite) of the front teeth. The prognathism is a hereditary variation that can be treated in mild to moderate forms at the start of treatment in children and young adults with some prospect of success. Cardinal treatment agent is the face mask (or Delaire mask) and in case of a narrow upper jaw the rapid maxillary expansion (RME). Treatment success is mainly dependent on further growth that is neither predictable nor sustainably influenced. However, a pronounced prognathism can be treated successfully only with the help of orthognathic surgery. Even if the prognathism is an imposing deviation from the average face, it does not imply a health risk. People with mandibular prognathism can get old and happy without therapy. The treatment need depends only on how far the individual feels affected aesthetically or functionally. Orthodontist never should try to urge people with mandibular prognathism to treatment.