Three cases of similar dentofacial deformities seen in two sisters and a brother are introduced and their orthodontic aspects considered. The first case showed excessive dentofacial deformity for which surgical orthodontic treatment was indicated, but at the patient\u27s request orthodontic treatment alone was attempted with unsatisfactory results. The second case presented asymmetrical skeletal mandibular protrusion, which was satisfactorily treated with surgical orthodontic methods. In the third case, satisfactory results were obtainable with orthodontic methods alone, because treatment was begun during the mixed dentition period. Had this patient not received treatment he would certainly have developed the same mandibular asymmetry exhibited by his elder siblings. The results of the third case suggest an effective role for orthodontic treatment in the prevention of dentofacial deformities, and underscore the importance of early treatment