A patient with chronic idiopathic mediastinal fibrosis (MF) without concomitant retroperitoneal fibrosis is reported. He presented with pleuritis, malaise and pain and stiffness in the thoracic spine. During the 3.5 years of observation no clinical signs of obstruction of adjacent visceral structures in the chest cavity have developed. The diagnosis was made by CT, X-rays of the chest remained normal throughout the observation period, except for thickening of the involved pleura. The administration of high doses of oral corticosteroids did not appear to influence either clinical symptoms or the manifestations of MF as seen by CT.