A case is presented of a 40 y.o. female with Cushing's syndrome. Her plasma glucocorticoid values were elevated (11-deoxy-cortisol: 3.46 ng/ml, cortisol: 25.6 micrograms/dl and cortisone: 35.7 ng/ml) with loss of diurnal variation. Urine 17-OHCS value failed to b suppressed by high dose dexamethasone and was unchanged after metyrapone administration. Her plasma mineral corticoids and androgens were within normal limits. There were 3 separate tumors in the right adrenal on CT and the left adrenal had no uptake on 131I-adosterol scintigram. We, therefore, diagnosed her illness as Cushing's syndrome due to unilateral multiple adenomas. Gross and histological examination of the right adrenal revealed one compact cell dominant adenoma and two clear cell dominant adenomas. This is the 4th case of Cushing syndrome due to unilateral multiple adrenal adenomas in Japan.