The patient, a 78-year-old female with a 10-year history of type 2 diabetes mellitus, was admitted to our department for evaluation of leg edema and general fatigue. Biochemical investigations revealed hypokalemia and elevated serum cortisol and plasma ACTH levels, with a loss of diurnal rhythm and failure of suppression at high doses (8 mg) of dexamethasone. No pituitary tumor or parasellar tumor was detected by contrast-enhanced computed tomography (CT) or magnetic resonance image scan of the pituitary. High resolution CT of the lung and bronchoscopic examination revealed no abnormalities. Abdominal and pelvic CT indicated bilateral, slightly diffuse, adrenal gland hyperplasia only. These findings led to a diagnosis of ACTH-dependent hypercortisolism from an undefined source. Ten days after admission the patient had a fever and was diagnosed with disseminated intravascular coagulation. Despite intensive treatment about 1 month after admission the patient died from progressive multiple organ failure. At autopsy, a histological examination of the periphery of the right middle lobe of the lung revealed the presence of tumorlets. Immunohistochemical staining of the tumorlets revealed scattered cells containing ACTH and many cells containing chromogranin A that were positive for Grimelius staining. In addition, multiple microabscesses were present throughout most tissues of the body. The ectopic hormonal production observed in the present case suggests that pulmonary tumorlets should thus be considered in the differential diagnosis of Cushing's syndrome, and medical treatment to inhibit steroidogenesis should be started immediately to reduce the risk of complications from hypercortisolism.