The study is based on a long-term cephalometric follow-up of lateral X-ray films of 48 boys with complete unilateral cleft lip and palate during puberty. The configuration of the face was negatively influenced by the reduced depth of the maxilla and limited vertical growth of the upper lip. As compared with the mandible, the maxilla grew less harmoniously in many respects; on the soft profile the depth of the nose increased most intensely. Retrusion of the maxilla led to a deterioration of sagittal intermaxillary relations in almost 92% of patients. In 32% of these patients the deterioration exceeded 3 of the ANB angle, and in 27% a transition from the 1st to the 3rd skeletal class was recorded. 25% of the subjects already belonged in class III at the age of ten years. In 94% of patients during puberty, flattening of the face occurred, which was frequently associated with a sunken upper lip (63%). Due to successful orthodontic treatment it was possible to restore maxillary overjet in 46% of the patients. In subjects who had a maxillary overjet of at least 2 mm at the age of 10 years, it did not change to negative values by the age of 15 years. Patients with more severe impairment of the jaws were treated more frequently by means of fixed appliances, but they did not differ substantially from the other patients in their further development (with the exception of a significant anteinclination of the palate).