Hyponatremia is a common electrolyte disorder related to central nervous system diseases and is often attributed to the syndrome of inappropriate antidiuretic hormon secretion (SIADH) and on the other hand to the cerebral salt wasting syndrome (CSWS). This syndrome is characterized by hyponatremia due to excesive renal sodium excretion resulting from a centrally mediated process. Given the divergent nature of the treatment it is of paramount importance for a clinician to be able to recognize and differentiate between these two entities. Thus the monitoring of renal function tests, which are needed for earlier diagnosis of effective osmolality disorders, is important to do in intensive care units, which are careing for patients with central nervous system leasons. Two patients succesfully treated for CSW due to ischemic stroke caused by arterial embolism from heart cavities are described.

        Key words: Hyponatremia - SIADH - CSWS - Ischemic stroke - Effective osmolality - Renal functi- on tests