Retroperitoneal fibrosis is an uncommon disease, characterized by the replacement of normal retroperitoneal tissue with fibrosis and/or chronic inflammation. In two thirds of the cases retroperitoneal fibrosis is idiopathic (IRF), whereas in the remaining ones it is secondary/associated to cancer, infections, drugs, autoimmune disease and vasculitis. IRF appears as a dense, fibrous plaque that usually arises between the level of the lower aorta and the common iliac arteries. As the plaque progresses, it engulfs the adjacent structures (e. g., ureters). In its early stages IRF is characterized by a rich infiltrate of lymphocytes, plasma cells and macrophages interspersed within fibroblasts and collagen bundles. In its advanced stages it becomes relatively avascular and acellular with abundant collagen bundles and scattered calcifications. The pathogenesis is unknown: some Authors suggest that IRF is a consequence of a local autoimmune reaction against atherosclerotic plaque antigens whereas others propose that it is the manifestation of a systemic autoimmune disease. The presenting signs and symptoms are non-specific; systemic manifestations (fever, anorexia, weight loss), often associated with local symptoms, are usually found to be related to the entrapment of retroperitoneal structures. The most common local symptom is lumbar and/or abdominal pain. The treatment can be surgical and/or medical: the former is required when obstructive complications are present; the latter, associated or not with surgery, can significantly improve the outcome of IRF patients and usually modifies the natural history of the disease. Steroids and tamoxifen are the most used drugs, whereas other agents such as azathioprine, methotrexate and cyclosporine are usually given to non-responder patients.