The aim of this study was to evaluate the effects of presurgical orthodontic correction of the mandibular prognathism. The sample consisted of two groups of surgical cases. The cases of the mandibular prognathism in group I with lower anterior dental compensation received presurgical orthodontic decompensation, and the cases in group II without lower anterior dental compensation did not receive presurgical orthodontic decompensation. The results showed that before presurgical orthodontic treatment, significantly differences existed between the two groups variable ILi/OL and ANB. After presurgical orthodontic correction lower incisors position in group I was very close to that in the group II, this means that the presurgical orthodontic treatment significantly changed the position of the lower incisors.