Craniosynostosis is a condition associated with the pathologic premature fusion of one or more cranial sutures. Physiologically, the metopic suture closes in infancy, while the remaining sutures close years later, even into adulthood. In craniosynostosis, characteristic calvarial deformity first appears on ultrasound in the second trimester and precedes identifiable suture fusion by 4–16 weeks. When this premature closure occurs, it is associated with restriction of calvarial growth perpendicular to the fused suture, with compensatory increase in growth at the remaining sutures. Previously there was debate as to whether the suture fusion itself drives this restriction of growth, or whether a cranial base deformity drives the abnormal development through tension bands in the dura. Currently there is a preponderance of evidence from human and rabbit studies supporting the idea that suture fusion is at least a significant contributor to the overall skull shape abnormality. The natural history of the disease is such that the deformity observed in infancy increases in severity if not surgically corrected.