Malformations of the central nervous system (CNS) are commonly encountered by the pediatric neurologist when called to evaluate a fetus or newborn. Such malformations may be isolated or appear as part of a genetic syndrome. In the past few years there have been great advances in identifying the genes and genetic alterations for many isolated CNS malformations and syndromes with CNS malformations. Therefore, it is important to look for associated anomalies in any infant with a CNS malformation, as well as consideration of the rest of the family. We have chosen four malformations (holoprosencephaly, hydrocephalus, lissencephaly, and schizencephaly) to serve as a paradigm for genetic malformations of the CNS. Understanding the underlying genetic etiology of a disorder allows us to give more accurate recurrence risk counseling, to better estimate potential complications, and to better manage the patient's care. As research continues, additional malformations and syndromes will be understood on the genetic level, and combining this genetic information with neurologic understanding will translate into better medical care for the patient. Copyright © 2001 by W.B. Saunders Company.