The purpose of this study was to examine the effects of the FR-3 appliance on the transversal dimension. The treatment group consisted of 20 patients with Class III malocclusion, who were treated with the FR-3 appliance. The control group consisted of 19 patients with Class III malocclusion. Posteroanterior radiographs and study models were taken at the beginning and at the end of the study in both groups. The results suggested that although FR-3 appliance therapy does not increase the width of the nasal cavity and does not stimulate the growth of the maxillary apical base, it does cause an increase in the intermolar and interpremolar distances in the maxilla both in the dental and the alveolar areas.