The two types of mesio-occlusion are developmental (true Class III) and acquired. 2. In acquired mesio-occlusion the mandible can be retruded comfortably so that maxillary and mandibular incisors meet edge to edge. This cannot be done by the patient with developmental mesio-occlusion. 3. The extent and severity of periodontal disease cannot be predicted from the severity of the malocclusion. 4. In most patients the treatment of choice for acquired mesio-occlusion is coronal reshaping and periodontal therapy if periodontal disease is present. 5. Orthodontic therapy may be used as an adjunctive therapy in selected patients. However, disadvantages are often greater than advantages when orthodontic therapy is used to treat acquired mesio-occlusion in adults.