A 50-year-old man was admitted to our hospital because of general malaise. Laboratory tests revealed severe hyponatremia (104 mEq/L), which was attributed to central adrenal insufficiency. To treat presumed central diabetes insipidus (CDI), we administered a small dose of hydrocortisone and gradually increased it to maintenance doses to prevent osmotic demyelination syndrome (ODS). Serum sodium levels did not increase more than 10 mEq/L/day and ODS did not occur. Thereafter, the patient was proven to have CDI. Incremental increases in glucocorticoid dose may reduce the risk of ODS for patients with hyponatremia due to central adrenal insufficiency, especially that complicated by CDI.