This case-control study supports the findings that retroperitoneal fibrosis persists longer than previously thought, and progression might even occur. Formerly uninvolved organs might become included in the process despite regression of the layer, leading to considerable problems if the condition is not treated in institutions familiar with this complex disease. We advocate a moderated follow-up scheme, as in the case of ordinary abdominal aortic aneurysm, and the need for long-term surveillance of inflammatory aneurysms.