Objectives: The purpose of this study was to assess cranial base and maxillary growth in patients with Class II- type I malocclusions when treated with Frankel?s functional regulator (FR-1b). Study Design: The treatment group was made up of 43 patients that were divided into two groups: prepubescent (n: 28), and pubescent (n: 15). The control group included 40 patients who did not receive any kind of treatment and were likewise divided into a prepubescent group (n: 19), and a pubescent group (n: 21). A computerized cephalometric study was carried out and superimpositions were done in order to assess the antero-posterior, vertical and rotational movement of the maxilla. Results: The results indicate that anterior cranial length is not affected by the regulator but the cranial deflection of the treatment group was diminished. Although a slight counterclockwise rotation effect on the upper jaw was observed due to treatment, no growth restriction of the maxilla in a vertical or antero-posterior direction was observed compared to other non-treated Class II-type I malocclusion patients. Conclusion: The functional regulator does not have any effect on anterior cranial length, but it does affect the angulation of the cranial base. According to our results, the appliance has demonstrated a flattening effect of the cranial base (p<0.05) in the treated sample. The functional regulator induces counterclockwise rotation rather than vertical or sagittal changes in the maxilla.