The most important perinatal encephalopathies, which are caused by diseases of the mother during pregnancy, comprise brain damage due to malnourishment and some inherited metabolic diseases, dysthyroidism and diabetes, infectious diseases, hypoxic circulatory disturbances and kernicterus. Besides the brain alterations directly caused by these conditions, changes of a secondary nature are discussed. These are mainly due to curtailed or perverted maturational and late developmental processes. The end-result thus will be a complex of primary and secondary changes and the type and distribution of alterations are dependent not only upon the nature of the harmful factor but also on the time of its operation.