Hyponatremia is a common complication of intracranial disease or surgery. An evaluation should be undertaken to determine whether cerebral salt wasting (CSW) or inappropriate secretion of antidiuretic hormone is present as a cause. Since the treatment principles are completely different in the two pathological states, differential diagnosis is very important. CSW is defined as the renal loss of sodium leading to hyponatremia and decreased extracellular fluid volume. In the literature, it has been noted that mineralocorticoid administration can be useful in CSW cases. We herein present an 11-year-old boy who developed hyponatremic seizures after intracranial tumor resection. He was diagnosed with CSW on the basis of high urinary sodium excretion and increased urine output, together with signs and symptoms of dehydration. Despite intensive fluid and salt therapy, we were unable to decrease the urinary output. Therefore, fludrocortisone therapy was administered and his urinary output and sodium excretion were decreased and his serum sodium level was normalized. In conclusion, in addition to fluid and salt replacement, mineralocorticoid supplementation also seems to be a safe and effective treatment for CSW. Copyright (C) 2001 S. Karger AG, Basel.