We report a rare case of Cushing's syndrome due to bilateral adrenocortical adenomas in a 45-year-old female. She suffered from diabetes mellitus and hypertension for a decade, but her appearance was not Cushingoid. The plasma cortisol level in the morning was at the upper limit of the normal range, but did not show a diurnal rhythm or was suppressed by 1 mg of dexamethasone. The plasma level of ACTH was undetectable, and it failed to respond to human CRH (hCRH). Plasma cortisol responded well to synthetic ACTH. The urinary 17-OHCS level was high, and was not suppressed by 4 mg of dexamethasone. While these findings were consistent with a diagnosis of adrenocortical adenoma, computed tomography showed several nodules in both adrenal glands that suggested the presence of huge nodular adrenocortical hyperplasia or bilateral adrenocortical adenomas. Bilateral adrenalectomy demonstrated the presence of three adenomas, two in the right and one in the left adrenal. Analysis of the extract from each adenoma revealed that two of the three produced an excess amount of cortisol. Magnetic resonance imaging (MRI) of the brain suggested the presence of pituitary adenoma. Prior to adrenalectomy, TSH, GH or LH showed a low response to TRH, GHRH or LHRH, respectively. Since normal responses were restored after bilateral adrenalectomy, these abnormalities were attributed to hypercortisolemia.