Familial diabetes insipidus is a rare occurrence. Paschkis, Rakoff, and Cantarow in their recent book "Clinical Endocrinology" state that 1 out of 70 cases was studied at the Peter Bent Brigham Hospital and none of 42 cases was studied at the University of Michigan. According to those authors: "The most impressive family tree contains 45 cases among 220 members of a family, in 5 generations. The transmission is probably through a dominant gene." Gates cites Weil's classic case reported in 1884, in which there were 23 affected (14 male and 9 female) in four generations. "The original progenitor was born in 1772 in Oberhessen [Germany] and had 220 descendants in five generations, 34 of whom had diabetes insipidus. Weil Jr. (1908) added 11 cases in the fifth generation of this family, making 34 cases (22 male-12 female) in five generations, the sibships numbering 34 affected: 46 normal. This is an