Affections of the nails are frequent in dermatologic practice, but the hereditary conditions are relatively uncommon. Moreover, they are interesting from the standpoint of genetics. In the family reported here, the deformity has occurred with considerable frequency, the defect being present in twelve cases through four generations. The onychoses may be congenital or acquired. The congenital types may consist of partial atrophy or complete absence. The etiology of the acquired types may be (a) inflammatory, (b) toxic, (c) parasitic or (d) trophic. Local causes are responsible for more than 50 per cent. of the cases of the disease. In every case of nail atrophy, syphilis should be ruled out by a Wassermann test, heredity by a careful history, and tinea infection by scrapings and cultures. Congenital dystrophy of the nails may be limited to the fingers or toes, or may involve both and may be apparent at birth, or appear