Wereport a case of adrenocorticotropic hormone (ACTH)-independent bilateral macronodular adrenocortical hyperplasia (AIMAH), which was successfully treated with mitotane.A 71-year-old man visited our hospital because of central obesity and enlarged bilateral adrenal glands. The endocrinological studies showed elevated plasma cortisol and undetectable levels of ACTH,a lack of suppression with high-dose dexamethasone and a hyper-response to exogenous ACTH. These clinical features were compatible with the diagnosis of AIMAH. In this patient, extra-adrenal multiple tumors were also detected. After treatment with mitotane, the plasma level of cortisol was decreased while that of ACTHwas increased and the signs of Cushing's syndrome were resolved. (Internal Medicine 38: 969-973, 1999)