The nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a rare, recently recognized disorder in water balance affecting not only infants but also adults. A new molecular mechanism responsible for NSIAD has recently been identified: a gain of function of the arginine vasopressin (AVP) receptor type 2 (V2R), causing the constitutive activation of the receptor. Clinical presentation and laboratory findings of NSIAD resemble those of the syndrome of inappropriate secretion of antidiuretic hormone and consist of hyponatraemia, seizures and the lack of urinary dilution; however, the AVP levels in plasma are undetectable or very low. An elucidation of the pathophysiology of this syndrome will provide more insight into the action of AVP. An effective treatment of NSIAD is available. It consists of fluid restriction and administration of oral urea. Reported experience with furosemide treatment in NSIAD is still lacking.