Cerebral salt-wasting syndrome is a disorder characterized by severe hyponatremia, volume depletion, and elevated brain natriuretic peptide but normal antidiuretic hormone levels. In this manuscript, we report the case of a six-year-old patient with cerebral salt-wasting syndrome associated with subacute sclerosing panencephalitis. The patient showed dehydration, tachycardia, pyrexia, polyuria, severe hyponatremia, and a significant loss of urinary sodium. He was successfully treated with sodium and fluid replacement therapy.