<h2>Summary</h2> Attention is directed to a group of three unusual congenital disorders to which surprisingly little reference has been made in the pediatric literature. The disorders are von Recklinghausen's neurofibromatosis, Bourneville's tuberous sclerosis, and angiomatosis of the brain associated with vascular nevi in the region of the distribution of the trigeminal nerve. All three conditions have been classified in the general category of neurocutaneous syndromes, after the suggestion of French observers. Recently, Yakovlev and Guthrie have proposed that the diseases be designated by the more descriptive term of "congenital ectodermoses." All three congenital disorders exhibit marked similarity in their clinical manifestations and in the character and distribution of their pathologic features. Furthermore, they involve electively organs, such as the nervous system, skin, retina, and eyeball, having their common origin in the ectodermal layer of the developing blastoderm. It should be borne in mind, however, that mesodermal hyperplasia, as is evidenced by the frequent presence of vascular nevi, may occur in varying degrees in all three congenital disorders either as a concomitant condition or obscuring entirely the ectodermal malformation. Although all three syndromes show invidual and characteristic manifestations, they are by no means mutally exclusive. They present signs and symptoms which overlap greatly and which exhibit an impressive range of variability: Of clinical interest is the occurrence of characteristic cutaneous anomalies which are indicative of associated maldevelopments in deeper seated, embryologically related structures, such as the peripheral and central nervous systems, and which affect usually the cephalic and caudal ends of the body. The cutaneous manifestations are not purely localized lesions, but are the external expression of widespread systemic maldevelopments which affect visceral, as well as somatic, structures. This is evidenced by the fact that at autopsy gross abnormalities, such as cysts and tumors, are found in other internal organs. Also of importance in this group of congenital disorders is the involvement of the entire nervous system and, in addition, the frequent occurrence of epilepsy and feeblemindedness. All three neurocutaneous syndromes show, furthermore, definite familial or hereditary tendencies. Von Recklinghausen's neurofibromatosis is a generalized disease involving primarily nervous tissue in any part of the body with secondary changes in other organs. Characteristically there may occur polypoid tumors of the skin, subcutaneous nodular tumors of the peripheral nerve trunks, lesions of the central nervous system and of the meninges, brownish pigmentation of the skin ("café au lait" spots), secondary changes in the skeletal system, and abnormalities of development of visceral structures. The disorder is not seen always in its complete form, various incomplete or abortive forms being present in which only one of the cardinal signs is manifest. Bourneville's tuberous sclerosis is a fairly rare congenital malformation and it is probably the most typical and clearly defined of the neurocutaneous syndromes in its clinical and pathologic features. It is a widespread disorder showing islands of hypertrophic sclerosis of the cerebral hemispheres, warty nodules of the face, the so-called "adenoma sebaceum," and cysts and tumors of internal organs. It is invariably associated with epilepsy and mental defect. The last of the group of neurocutaneous syndromes, is the clinical picture of angiomatosis of the brain associated with vascular nevi in the region of distribution of the trigeminal nerve (encephalotrigeminal angiomatosis). Although, at first sight, it consists of congenital malformation of blood vessels, a tissue of mesodermal origin, evidence is in favor of the fact that it is of neurogenic (ectodermal) origin. It should be emphasized that vasuclar newgrowths of the brain are divisible into two major groups, the angiomatous malformations which consist of nervous and vascular tissue, and the angioblastomas or true neoplasms which are composed solely of mesodermal tissue. The latter involve primarily the cerebellum and have been known under the name of Lindau's disease. They may be either solid or cystic in structure and are accompanied frequently by malformations of visceral organs and vascular newgrowths of the retina (von Hipple's disease), but no nevi of the skin. This condition should be clearly differentiated from the angiomatous malformations which are also accompanied by general systemic malformations and by vascular nevi of the skin, as well as puphthalmus (glaucoma). Often the congenital nevi of trigeminal distribution are associated with calcified homolateral angiomatous malformations of the brain, usually of the occipital area. Three case reports have been presented, two of them as illustrations of the varied clinical manifestations of the complicated disorder of von Recklinghausen's neurofibromatosis, and one of them as an example of angiomatous malformation of the brain in association with vascular nevi of trigeminal distribution.