Although it is currently thought that surgery is indicated mainly for cosmetic reasons in isolated craniosynostoses, the functional aspects of the treatment must not be underestimated. Prospective studies on intracranial pressure and mental evolution of these children have shown that there were functional consequences in a significant proportion of cases even of single suture fusion. The frequency of increased intracranial hypertension and the risk of mental impairment depend on the age of the child and the type of craniosynostosis. In nonsyndromic cases, the higher risks are observed in multisutural craniosynostoses (brachycephaly, oxycephaly). In syndromic cases, the risk of intracranial hypertension is higher in Crouzon syndrome, and Apert syndrome carries the higher risk of mental retardation. The study of a personal series of 2,137 craniosynostoses shows that the functional and the cosmetic results are better after early surgery, and that the operative risks are not higher in infants than in older children.