A boy (Hellman dental age III B) with mandibular prognathism was treated by means of the labiolingual appliance and the chin cap. Following results were obtained; 1) Except the problem of development, most of treatment objectives were achieved after 8 months of active treatment. 2) The axial inclinations of upper and lower incisors were changed by the treatment. 3) The most notable change was the reduction of genial angle. 4) The patient has retained the good occlusal stability till after 18 months of retention.