Congenital nephrogenic diabetes insipidus (NDI) is a rare cause of hypernatremia in newborns. Central diabetes insipidus (CDI) is the main differential diagnosis in NDI, however NDI responds poorly to desmopressin acetate (DDAVP) treatment, while this is the mainstay of CDI management. Therefore, early and correct diagnosis of NDI is important to avoid the complications of inappropriate therapy. We report a newborn with hypernatremia and hypotonic polyuria. The patient was initially responsive but subsequently unresponsive to intranasal DDAVP treatment in terms of both urine output and serum sodium levels. A novel hemizygous missense mutation (c.632T>
C, p.L211P) in the