Aicardi syndrome is an X-linked dominant disorder, which is characterized by the diagnostic tetrad of infantile spasms, chorioretinal lacunae, mental retardation, and agenesis or hypogenesis of the corpus callosum. The syndrome is seen almost exclusively in females, since early embryonic lethality is observed in males. The mutation forms a balanced translocation of the X chromosome. The patients with Aicardi syndrome present with early-onset infantile spasms, severe mental retardation, severe limitation of motor development and language, and a prognosis of survival for only a few months or years. Aicardi syndrome should be considered as a syndrome in which the clinical findings and prognosis are heterogeneous. Intracranial anomalies include callosal agenesis or hypogenesis, which is typically associated with interhemispheric cysts, absence of the septum pellucidum, agenesis of the anterior commissure, abnormal orientation of the hippocampal formation, gray matter heterotopia, cortical dysplasia, pachygyria, colpocephaly, posterior fossa cysts, cerebellar hemispheric and vermian hypoplasia, choroid plexus papillomas and cysts, optic nerve and chiasmal hypoplasia, and microphthalmia. The type of cortical dysplasia in Aicardi syndrome differs from the classical four-layered microgyria. Neuropathological examination of the brain shows unlayered polymicrogyria that differs from the classical four-layered polymicrogyria, and is similar to cortical anomaly encountered in the so called "cobblestone" lissencephaly. The study of the polymicrogyric cortex with the Golgi method reveals an abnormal orientation of neuronal dendritic tree in the superficial area along the fused molecular layers. Myelination may be delayed in the patients. Ophthalmologic examination reveals characteristic chorioretinal lacunae, which result from retinal dysplasia, anomalous retinal vessels, posterior scleral ectasia, a peripheral fibrous ridge and retrobulbar ocular colobomata. Costovertebral malformations such as hemivertebrae, scoliosis, and absent or malformed ribs may also be associated with Aicardi syndrome.