This cephalometric study evaluated skeletal and dentoalveolar changes produced by rapid maxillary expansion and facial mask therapy in 85 subjects exhibiting a Class III malocclusion with a retruded maxilla. The skeletal maturity of individual patients was assessed on the basis of Fishman's skeletal maturity indicator (SMI), using hand-wrist radiographs at the initiation of treatment, to determine the relationship between the effect of maxillary protraction and skeletal age. Patients were divided into three groups: prepubertal growth peak group (SMI 1-3), pubertal growth peak group (SMI 4-7), and postpubertal growth peak group (SMI 8-11). The major findings of this cephalometric study were as follows: (1) there was no difference in the effects of maxillary advancement after maxillary protraction between the prepubertal growth peak and the pubertal growth peak group, but there was a decrease in the postpubertal growth peak group; (2) in the postpubertal growth peak group, there was a decrease in maxillary skeletal advancement, whereas the dentoalveolar effect was increased; (3) the posteroinferior rotation of mandible, the increase of lower facial height, and the eruption of maxillary molars showed no correlation with skeletal age. The results of our study emphasize the importance of performing a biologic evaluation of skeletal maturity and pubertal growth peak in individual patients in the diagnosis and treatment planning of Class III malocclusions.