Malformations of the central nervous system (CNS) are evaluated and treated by pediatric neurosurgeons. There is a spectrum of morphological variations within each type of malformation and with associated features that may determine whether the defect is isolated or part of a syndrome. Alterations in the normal sex ratio have been found in many malformations of the CNS but the reasons for them are usually unclear. It can be reasoned that some CNS malformations would have unusual sex ratios by chance alone. However there are recurrent patterns. When there is a dominance of one sex for a particular malformation, this information can help predict the likelihood of the malformation in a patient and influence diagnostic approaches. The present report provides information on selected CNS malformations that have altered sex ratios.