Six cases of idiopathic fibrosis are presented to demonstrate the different manifestations of the disease and the efficiency of CT and MRI. In addition to the most common form, retroperitoneal fibrosis (Ormond's disease), fibrosis was seen in the mediastinum and pelvis. The inflammatory aortic aneurysm is a special variant. MRI was superior to CT in many diagnostic requirements. The extent of fibrosis was demonstrated more sensitively and MRI showed sclerosis in regions that appeared normal on CT. Occlusion of large vessels and collateral circulation were better depicted on MRI. The superior tissue contrast of MRI permitted differentiation of several stages of inflammation, which is of major significance for treatment and follow-up.