Hyponatremia is a common electrolyte disturbance following intracranial disorders. Hyponatremia is of clinical significance as a rapidly decreasing serum sodium concentration as well as rapid correction of chronic hyponatremia may lead to neurological symptoms. Especially two syndromes leading to hyponatremia in intracranial disorders need to be distinguished, as they resemble each other in many, but not all ways. These are the syndrome of inappropriate ADH secretion (SIADH) and the cerebral salt wasting syndrome (CSW). The syndrome of inappropriate ADH secretion is characterized by water retention, caused by inappropriate release of ADH, leading to dilutional hyponatremia. The cerebral salt wasting syndrome on the other hand, represents primary natriuresis, leading to hypovolemia and sodium deficit. SIADH should be treated by fluid restriction, whereas the treatment of CSW consists of sodium and water administration. However, in the literature there is abundant evidence that hyponatremia in intracranial diseases is mostly caused by CSW. Therefore, treatment with fluid and salt supplementation seems indicated in patients with intracranial disorders who develop hyponatremia and natriuresis.