A case is described in which a Class II malocclusion with severe Class II skeletal pattern was treated with a modified Twin Block Appliance. The patient, an 11-year-old girl, had initially presented with an ameloblastoma located in the right maxilla. The subsequent defect produced by surgery was obturated by the appliance during her orthodontic treatment, which was undertaken during her pubertal growth spurt. Two years later the result was stable, allowing the provision of a more definitive prothesis to restore the occlusion.