The present study attempts to evaluate cephalometrically the effects of Frankel's function regulator (FR-4) appliance on the treatment of Angle Class I skeletal anterior open bite malocclusion. Forty Turkish children (26 girls and 14 boys), with Angle Class I skeletal anterior open bite, were randomly divided into two groups of 20 (13 girls and 7 boys). Patients who had not undergone treatment served as the control group, whereas a second group was treated with lip-seal training and the FR-4 appliance. Chronologic mean decimal age at initial period of the investigation was 8.7 years in the treated group, and 8.9 years in the control group. Treatment and observation periods were 2 years. Investigation was carried out on lateral cephalograms taken before and after the study period. The results indicate that a spontaneous downward and backward growth direction of the mandible observed in the control group could be changed to a upward and forward direction by FR-4 therapy. The skeletal anterior open bite was successfully corrected through upward and forward mandibular rotation.