We report a case of adrenal black adenoma associated with Cushing's syndrome. A 41-yr-old man presented to our hospital with a 6-yr history of severe hypertension and general fatigue, and a 1-mo history of diabetes mellitus. Physical examination disclosed cushing-oid manifestations. His serum cortisol concentrations ranged from 14.0 to 15.4 microg/dL, with an ACTH level <5 pg/mL. Urinary free cortisol level was increased (125 microg/d). Cortisol was not suppressed on the overnight 1 mg oral dexamethasone suppression test (DST), 2-d low-dose DST, and 2-d high-dose DST. Abdominal computed tomography and magnetic resonance imaging studies revealed a solid round tumor approx 3 cm in diameter, located in the left adrenal gland. Left adrenalectomy was performed; the surgical specimen revealed a black ade-noma consisting of compact cells within numerous pigments that seemed to be lipofuscin in nature.