A 72-year-old man was admitted to our hospital because of a tumor-like shadow on a chest X-ray film. At the initial examination, he had clinical signs of Cushing's syndrome: moon face, central obesity, and hypertension. A computed tomographic scan of chest showed an abnormal shadow in the lung (5 x 6 cm) with involvement of the right paratracheal and anterior tracheal lymph nodes, and a right-sided pleural effusion. Small cell lung cancer (extended disease; T2N2M6 stage IV) was diagnosed after a transbronchial biopsy. The concentrations of adrenocorticotropic hormone, cortisol, and parathyroid hormone in plasma were markedly elevated, and there was no circadian rhythm (336 pg/ml. more than 60.1 micrograms ml. and 805 pg/ml, respectively). Fluid obtained by thoracentasis had malignant cells, and the levels of adrenocorticotropic hormone and parathyroid hormone in the effusion (1120 pg/ml and 1810 pg/ml, respectively) were higher than those in serum, which indicates that these hormones were produced by the tumor cells. The patient received chemotherapy and responded well, but he died of respiratory failure 26 months later. The response rate to chemotherapy in elderly patients with lung cancer is said to be comparable to that in younger patients, but treatment may be difficult because of poor performance status and diminished physical capacity. Although patients with lung cancer complicated by Cushing's syndrome have a poor prognosis, this patient survived for more than 2 years after the disease was diagnosed.