Retroperitoneal fibrosis is a connective disease of the auto-inflammatory/auto-immune type of the retroperitoneum with unknown etiology and pathological mechanism. The manifestations of the pathology can be local or systemic. Amongst the local symptoms, the dull and constant pain in the hips, back or abdomen is the most frequent. We report here a case of a 47-year-old woman, whose pathogenic mechanism could be related to an "IgG4-related disease" disorder as suggested by an increased serum level of this subclass of IgG and the positive immunohistochemistry. The diagnosis is not easy, because this pathology generates masses; adenomegalies with retro peritoneal development, that makes it similar to lymphomas or metastases from ovarian tumors.