The aim of this paper is to present a new functional appliance named 'SOS activator. 'It is a modified removable headgear-activator type of appliance, which is indicated in growing skeletal Class II cases with mandibular retrusion and can be combined with banded (Quad-Helix, Hyrax, TPA) and bonded fixed appliances in the upper arch. This device can concurrently correct sagittal, vertical, and transversal discrepancies allowing the active expansion of the upper dental arch and the alignment of the upper teeth, while providing maximum anchorage or even distal movement of the upper first molars and exerting a restraining effect on the maxilla. The use of this appliance eliminates the need for a first phase of therapy and shortens treatment duration. In clinicalpraxis the 'SOS activator' has been used until now for the treatment of hundreds ofpatients and seems to be a reliable method of choice for the correction of Class II malocclusions with a retrognathic mandible, while presenting many advantages compared to other functional appliances. In this paper, the technical characteristics, the construction details, and the method of action of the new device are analyzed Furthermore, a treated case with this method is presented.