The authors present their experience of maxillo-mandibular osteotomies performed at the Charles Nicolle Hospital in Tunis. The objective of this paper is to describe the preliminary steps (clinical, radiographic, photographic, modelling, cephalometric) in order to obtain a precise diagnosis of the dysmorphosis. They use Burstone's cephalometric analyses which allow evaluation of the relations between soft tissues which do not correspond to the relations of bony and dental displacement. They also present several clinical cases, the pre-operative steps and, most importantly, Burstone's cephalometric analyses demonstrating that, after osteotomies, the cephalometric values for soft tissues approach normal values. Complete analysis of the naso-maxillary profile may correct the motivation for consultation in some cases. The indication for Lefort I osteotomy is sometimes more appropriate than rhinoplasty. Preoperative orthodontic preparation is often required. Functional rehabilitation is necessary to adapt the orofacial muscles to the new shapes of the dental arch and to prevent recurrence.