The purpose of this study was to examine mandibular morphology and growth in patients with Crouzon, Pfeiffer, and Apert syndromes using posteroanterior cephalograms. Fifteen patients with Apert (n = 2), Crouzon (n = 11), and Pfeiffer (n = 2) (11 female, 4 male) syndrome were included in this study. All patients had serial posteroanterior cephalograms at 5, 10, and 15 years of age. The bicondylar width, bigonial width, bicondylar/bigonial ratio, and ramus to intercondylar plane angle for each patient were measured on the cephalograms and compared with age-match controls. An analysis of variance analysis was carried out to detect differences between patients and controls and sex differences between patients. In both male and female patients, there was a statistically significant reduction in bicondylar width compared with age-matched controls. Male patients also had a statistically significant increase in bigonial width compared with controls and female patients at 10 and 15 years. The resulting bicondylar/bigonial ratios were significantly reduced, and the ramus to intercondylar plane angles were significantly increased in both male and female patients compared with controls. Unlike previous reports of patients with syndromic synostosis, this study demonstrates that the mandible has significant morphologic and growth abnormalities, including constriction of bicondylar width with near normal bigonial width in female patients. These findings suggest a narrowing at the cranial base with resulting restriction of normal transverse mandibular growth at the condyle. The secondary nature of the mandibular finding is suggested by the near normal or increased transverse growth at the gonion in females and males, respectively. Consequently, the ramus appears torqued inward, forming a greater angle with the cranial base.