A 75-year-old female is referred for evaluation of a progressive leg swelling. Angiological and MRI evaluation show the presence of inflammatory tissue surrounding the aorta and the left iliac vessels, causing significant stenosis. Upon suspicion of retroperitoneal fibrosis, we actively seek for secondary causes such as malignancies, autoimmune diseases and infections, as well as IgG4-related disease. All investigations result negative and we make the diagnosis of idiopathic retroperitoneal fibrosis. Steroid therapy was started and we observed a rapid amelioration of symptoms and radiological disappearance of the inflammatory tissue around the aorta.