There are congenital malformations affecting more or less electively the ectodermal structures, i. e., the nervous system, the skin, the retina, the eyeball and its contents; sometimes visceral organs are also involved. As these congenital malformations, in many instances, are associated with mental defect and with epilepsy, we thought that such cases deserve to be studied as a special group. As we realize the difficulties inherent to a subject that involves the most intricate problems of embryology and developmental histopathology, we shall limit ourselves to the presentation of a series of case records, and, on the ground of arguments derived from the literature and supported by our own clinical observations, we shall make tentative suggestions. These will include considerations as to the nature of these neurocutaneous syndromes, their mutual relationship and their relationship to the associated neurologic and psychic manifestations, i. e., epilepsy and mental defect. Three types of neurocutaneous