Objective : Le Fort III osteotomy with distraction osteogenesis (DO) is used to improve the retruded midface in patients with Crouzon or Apert syndrome. This study aimed to evaluate sagittal and vertical preoperative and postoperative cephalometric changes of DO of the midface in patients with Crouzon or Apert syndrome. Design : Population-based case-control study. Patients and Methods : Records of patients with the syndrome of Crouzon (N = 6) or Apert (N = 7) were compared, before and after Le Fort III DO, with a nonsyndromic untreated control group (N = 486). Main Outcome Measures : Sagittal and vertical cephalometric maxillary landmarks and measurements were used to predict and measure midface advancement and rotation after Le Fort III DO. Cephalograms were taken before surgery (T0), 4 months after surgery at removal of the distraction device (T1), and 1 year after removal of the distraction device (T2). Analysis : Z scores were performed to compare cephalometric measures of syndromic patients with control subjects. Results : Cephalograms of 13 patients with Crouzon syndrome (N = 6) or Apert (N = 7) (age range 8.2 to 19.8 years) were evaluated. Treatment changes (T1-T2) showed statistically significant maxillary advancement, with no significant differences between the patients with the Crouzon or Apert syndrome. Conclusions : DO of the midface in patients with Crouzon or Apert syndrome seems to be stable in the sagittal direction after follow-up. Although Crouzon and Apert differ after DO, anteroposterior craniofacial dimensions were significantly improved and were closer to patterns of normal subjects.