A 53-year-old female had clinical and laboratory findings suggestive of Cushing's syndrome. In contrast to the Cushing's syndrome caused by cortical adenoma, a high level of urinary 17-ketosteroids (17-KS) was also noted. Imaging studies revealed a right adrenal tumor. Right adrenectomy was performed; the surgical specimen revealed a black adenoma consisting of compact cells with numerous pigments which seemed to be lipofuscin in nature. The present case indicates that black adenoma as well as adrenocortical carcinoma should be suspected, when patients with Cushing's syndrome show an increased level of urinary 17-KS excretion.