The purpose of this work was to provide a comprehensive description of craniofacial alteration in the Class III patient in response to orthopedic chin cup treatment. Thirty patients with skeletal Class III malocclusion under treatment with the chin cup appliance, averaging 6 years of age at the start of treatment, were followed longitudinally for a 3-year period. This treatment sample was compared cephalometrically with an analogous untreated Class III sample. The following significant craniofacial alterations were noted in the sample that underwent orthopedic chin cup therapy: 1. 1. A retardation of vertical ramus growth. 2. 2. A retardation of vertical development in the posterior aspect of the mandibular body. 3. 3. A retardation of vertical development in the posterior maxilla. 4. 4. A closure of the gonial angle. 5. 5. A distal rotation of the mandibular complex. 6. 6. A decreased amount of anteroposterior anterior cranial base growth. 7. 7. A redirection of the predominantly horizontal mandibular growth pattern to a more vertical direction. 8. 8. A reduction of the maxillomandibular malrelationship toward normative values. 9. 9. A production of an Angle Class I dental relationship following the establishment of normal maxillomandibular relations. 10. 10. A lack of detectable localized effect on the symphyseal region or incisor position as a direct result of chin cup placement and pressure. 11. 11. Development of soft-tissue profile changes in harmony with underlying skeletal changes. While all of the listed alterations are important when analyzed separately, they gain increased importance when considered together. With orthopedic chin cup therapy, there is a change in craniofacial pattern leading to the observed resolution of the Angle skeletal Class III malocclusion. This study thus provides strong support for the use of the orthopedic-force chin cup appliance in the clinical management of young patients with skeletal mandibular prognathism.