A 64-year-old woman was admitted for evaluation of hyponatremia. She was maintained on hypertonic saline administration. Without this therapy, the serum Na concentration decreased progressively to 127mEq/L and the plasma osmolality to 254 mOsm/Kg H₂O, on Day 3. At that time, the concentration of antidiuretic hormone (ADH) was as high as 3.5pg/ml. A skull radiogram revealed an enlarged sella turcica. Computed tomography (CT) revealed a low density in the sella, and magnetic resonance imaging revealed equal intensity of the sella turcica and the cerebrospinal fluid. A diagnosis of empty sella syndrome was made by metrizamide cisternography in conjunction with CT scanning. A diagnosis of panhypopituitarism was made by endocrine function tests. ¹²³I-thyroidal uptake was 6% when her serum TSH was10.9μU/ml, suggesting that she might also have primary hypothyroidism. When this patient was given glucocorticoid before levothyroxine replacement, her serum Na concentration rose up to about 140mEq/L and a normal relationship between her plasma ADH level (2.4pg/ml) and plasma osmolality (281 mOsm/kg H₂O) was restored. Therefore, it was suggested that ADH hypersecretion induced by the glucocorticoid deficiency might in part contribute to the development of hyponatremia. This is the case of primary empty syndrome associated with panhypopituitarism, in whom initial symptom was caused by hyponatremia.