Two adrenal tumors were incidentally discovered in the patients with dawn hypertension. They had no clinical features of Cushing's syndrome. These cases were regarded as pre-Cushing's syndrome by endocrinological evaluation. After adrenalectomy, the adrenal hormone regulation was normalized and dawn hypertension disappeared. Our findings suggest that dawn hypertension is a typical clinical sign of pre-Cushing's syndrome and this syndrome may represent a premature status of Cushing's syndrome.