In the practice of pediatrics many children are examined because of backwardness of development. A number of well recognized clinical types are presented, such as mongolism, microcephaly and oxycephaly. For most of these unfortunate children one can do little therapeutically. One may, however, help the parents by giving them as accurate prognoses as possible. Many of the abnormalities are not familial, and the chance of their recurrence is extremely small. Some types, however, do occur more than once in the same family and generation. This is true of progressive subcortical encephalopathy (Schilder's disease), of amaurotic idiocy, of diffuse infantile cerebral sclerosis as described by Krabbe1 and of a slightly different form reported by Pelizaeus2 and by Merzbacher.3 Penfield and Geyelin4 described a familial cerebral calcification with epilepsy. Hereditary chronic progressive chorea (Huntington's) and the spinal form of hereditary sclerosis (Friedreich's ataxia) are well known examples of