Congenital nephrogenic diabetes insipidus is a rare hereditary disease characterized by a renal insensitivity to circulating vasopressin. Genetic linkage studies have demonstrated that the gene responsible for congenital nephrogenic diabetes insipidus is located in region 28 of the X chromosome long arm. That the gene coding for the vasopressin V2 receptor is also located in the q28-qter of chromosome X suggests that the signalisation defect in congenital nephrogenic diabetes insipidus is at the level of the receptor itself. Indeed, congenital nephrogenic diabetes insipidus is a genetically heterogeneous disease since several point mutations in the vasopressin V2 receptor gene nucleotide sequence have been observed in different families of afflicted patients. Moreover, the observation that one of these mutations leads to a lack of cyclic AMP production in response to vasopressin confirms that mutations of the vasopressin V2 receptor sequence are the molecular defects responsible for congenital nephrogenic diabetes insipidus.