A girl 16 7/12 years of age with Cushing's disease secondary to pituitary microadenoma is described. The tumor was very clearly demonstrated by high-resolution contrast-enhanced computed tomography (CT) with thin slices and was removed by transsphenoidal microadenomectomy. In some patients with Cushing's disease levels of ACTH and cortisol are not always high. Therefore, high-resolution contrast-enhanced CT with thin slices should be performed when the diagnosis of Cushing's disease is suspected even when the definite diagnosis cannot be established by endocrinological examinations.