This article reviews the data on the effects of synostosis on cognitive development and the role of surgical intervention in ameliorating these effects. The literature on children with single-suture craniosynostosis, treated both surgically and conservatively, is reviewed. The evidence for possible pathophysiological mechanisms by which brain restriction might affect cognitive development is also reviewed. Although children with single-suture isolated craniosynostosis may be at risk of developmental delay, learning disability, or both, especially with regard to speech or language skills, available testing methodologies provide no evidence of an association between surgical intervention and ultimate intellectual outcome. Despite the controversies about the role of surgery in addressing the cognitive sequelae of simple craniosynostosis, in the absence of definitive data, the indications for surgery include correction of deformity and minimization of cognitive sequelae. The relative risks of performing surgery early or late must be determined on an individual basis, balancing potential cosmetic and cognitive benefits against the heightened risk of reoperation or perioperative morbidity.