Nephrogenic diabetes insipidus has been cited as one of the causes of mental retardation. Since the course of the disease and the severity of the symptoms can be influenced by the nature of the diet, the intake of water, and more recently by drug therapy, information concerning psychological development in this disease is of importance. A review of available literature reveals a curious paucity of published psychometric data concerning the development of these children. Almost all of the reports refer to the developmental status of young children. Kirman et al.1 reported two cases of nephrogenic diabetes in[ill] sipidus in which formal psychological tests revealed severe mental retardation in one and moderate retardation in the other. Guard2 reported one case of a child functioning at the borderline mental defective level, but it appears that other factors may have affected the child's intellectual functioning at the time of examination.