Retroperitoneal fibrosis (RPF) is characterised by inflammatory fibrotic processes affecting the retroperitoneal structures. Its prevalence of 1 - 2/200,000 makes it a rare disease. To date, there are no guidelines for the diagnosis of or therapy for the disease. If untreated, the disease may be fatal. In 2006, the Department of Urology of the HELIOS Klinikum Wuppertal undertook to establish a nationwide patient registry, which would facilitate prospective therapy trials and the drafting of recommendations for diagnostic procedures. The pathogenesis of the disease is still unclear. Since some RPF-patients present with associated autoimmune diseases, autoimmune processes are suspected to play a role in causing the disease. The presence of autoantibodies and histological similarities with vasculitis support this hypothesis. Following initial general symptoms, patients display localised symptoms (flank pain, leg oedema, abdominal discomfort), caused by the displacing effect of the fibrotic plaques. Laboratory tests show elevated ESR and C-reactive protein and in some cases a moderate anaemia. Histological examinations should be undertaken to rule out the presence of malignant tumours. Radiological diagnostics (excretory urography, CT, MRI) show a retroperitoneal mass which blocks, compresses and displaces, completely or in part, the large vessels and the ureter. Initial therapy aims at restoring the function of the affected hollow organs through the application of (ureteric) stents, followed by immunosuppressive therapy. If drug therapy is unsuccessful, surgical procedures will follow to protect the ureter from compression. In some cases, ureteral replacement or an autotransplant of the kidney may be necessary. Life-long observation of the patients is necessary, as the disease may be chronic and relapsing. Interdisciplinary and nationwide cooperation is of crucial importance to further investigate this disease.