INTRODUCTION: Retroperitoneal fibrosis (RPF) is a rare disorder characterized by the sheathing of retroperitoneal structures by fibro-inflammatory process. It can be either isolated or associated with an underlying disease or condition. In the absence of consistent and consensual approach, the objective of this study was to assess the relevance of diagnostic tests performed during the diagnostic work-up of RPF. METHODS: Seventy-seven patients were included in this retrospective multicenter study. The diagnosis of RPF was defined by the presence of a thickened circumferential homogeneous tissue unsheathing the infrarenal aorta, excluding peri-aneurysmal fibrosis and a clear evidence of a cancer. RESULTS: In 62 cases (80.5%), the RPF was considered as being primary or "idiopathic". Surgical (n=31) or CT-guided (n=9) biopsies of the RPF were performed in half of the patients showing some fibrotic or non-specific inflammatory lesions in 98% of cases. A bone marrow biopsy was performed in 23 patients leading to diagnosis of low grade B cell non-Hodgkin lymphoma in a single patient who also had a monoclonal gammopathy IgM. The systematic search for autoantibodies or serum tumor markers was of no diagnostic value. CONCLUSIONS: Although the diagnostic procedure was heterogeneous, no cause or associated disease was found in the majority of cases of FRP in this series. In the absence of any clinical or paraclinical evidence suggesting an underlying disease or any atypical features at presentation, a number of non-invasive tests (autoantibodies, tumor markers, bone scintigraphy) and also more invasive diagnostic tests (bone marrow and RPF biopsies) seem of little relevance.