To assess the stability of mandible position after orthognathic surgery for correction of class III skeletal malocclusion. Twenty adult males, aged 18 to 40 years, with Angle class III skeletal malocclusion underwent preoperative orthodontic treatment for elimination of dental compensations followed by combined maxillomandibular surgery with rigid internal fixation. Lateral cephalograms from each patient, obtained in the natural head position before surgery, immediately after surgery, and at 6-month follow-up, were retrieved from the files of the Pontifical Catholic University of Rio Grande do Sul outpatient Oral and Maxillofacial Surgery clinic and compared. Comparison of craniometric landmark measurements showed that the precision of mandibular setback was compromised in the horizontal plane, with a mean mandibular relapse of 37.75% at point B and 45.85% at point Pg. Improved intercuspation and adaptation of the musculature to the new position of the jaws after orthognathic surgery lead to counterclockwise rotation of the mandible, ultimately displacing the mandible more anteriorly than desired.