The advances in our understanding of the pathophysiology of defects in the antidiuretic hormone, the V2 receptor and the water channel, owing to mutations in the prepro-AVP-NPII, AVPR2 and AQP2 genes respectively, is providing insight into inherited diabetes insipidus as well as the more numerous sporadic cases. Further structure-function analyses of these mutated genes will increase our understanding of normal vasopressin-regulated water transport across the kidney epithelium at the molecular level.