Lissencephaly, which literally means smooth brain, is a rare brain formation disorder caused by defective neuronal migration during the 12th to 24th weeks of gestation, resulting in a lack of development of brain folds (gyri) and grooves (sulci). It is a form of cephalic disorder. Children with lissencephaly are severely neurologically impaired and often die within several months of birth.

Affected children display severe psychomotor retardation, failure to thrive, seizures, and muscle spasticity or hypotonia. Other symptoms of the disorder may include unusual facial appearance, difficulty swallowing, and anomalies of the hands, fingers, or toes. Causes of lissencephaly can include viral infections of the uterus or the foetus during the first trimester, or insufficient blood supply to the foetal brain early in pregnancy.