A 42-year-old woman was referred to our hospital for evaluation of severe hypertension. A right adrenal tumor was revealed by CT scan, and the elevation of cortisol and u-17OHCS was found. We made a diagnosis of adrenal adenoma with Cushing's syndrome and performed right adrenalectomy. However, a small myelolipoma (1.5 mm in diameter) was found beside the cortical adenoma by histopathological examination. Adrenal myelolipoma is not a rare disease now, because it is easily-detected as an incidental by CT scan. The present case of adrenal myelolipoma, however, is interesting and uncommon in its connection with functioning cortical adenoma. Only 3 cases have been previously reported so far in English and Japanese publications. We discuss the etiology of adrenal myelolipoma, and suggest that myelolipoma would develop in the course of regressive or necrotic degeneration of cortical cells by hormonal disorders, stress, circulatory disturbance or other unknown factors.