During his last routine pediatric visit, a 4-month-old boy with a large head circumference (98th percentile for his age) was referred for radiographic evaluation. The infant had been delivered by cesarean birth because of cephalopelvic disproportion; his head size had gradually increased since birth. There was a family history of this condition. A radiograph demonstrated the absence of a large central portion (primarily the frontal and parietal portions) of the calvarium. The lack of ossification in this area resulted in a dramatically enlarged anterior fontanelle. Widening of the coronal sutures and right lambdoid suture was also noted. These findings are consistent with the midline fusion anomalies typically seen in cleidocranial dysostosis. Douglas P. Beall, MD, of Oklahoma City and John Whyte, MD, of Rockville, Md, write that this autosomal dominant disorder affects both sexes equally. The gene responsible for the manifestations of cleidocranial dysostosis is located on chromosome 6 at the 6p21 locus. Characteristic findings include delayed ossification of midline bones, with multiple ossification centers (wormian bones), and hypoplasia/aplasia of the clavicles, usually the outer third. The skull is abnormally shaped, and there is typically depression of the sagittal suture. Patients usually have a protruding jaw, wide nasal bridge, and heavy brow. The thorax is narrow and may be bell-shaped. Joint laxity is also possible. Typically, patients are short—a result of abnormal enchondral ossification. No preventive measures or specific treatments are available for patients with cleidocranial dysostosis. Dental abnormalities—the main complication in these patients—can result from malalignment of the teeth and retention of deciduous teeth. Mental development is normal.