Genioplasty is a treatment method of the long face syndrome by reducing the lower face height to be equal, on lateral cephalometric radiography, to 55% of the total height of the anterior face whereas the height of the upper face is equal to 45% of this one (Wylie). Surgical technique described in this paper is particular by making up a tenon and mortise joint allowing a good stability of the lower fragment of osteotomy whose muscular insertions are preserved. Its effects are simultaneously functional and cosmetic because the oral musculature disorder is suppressed while chin aspect is modified.