Abstract Immunoglobulin G4 (IgG4)‐related disease (IgG4‐RD) is a multi‐organ immune‐mediated fibroinflammatory disorder that may imitate malignancy, infectious or any other inflammatory disorder. IgG4‐related retroperitoneal fibrosis (IgG4‐RPF) is a rare form of IgG4‐RD, diagnosis of which is often relied on radiological technology. Herein, we describe a case of 60 year old male, presenting with low back pain and weight loss for a period of 2 months and 15 days. Imaging studies showed a retroperitoneal tumorous mass along with bilateral hydroureteronephrosis, which was later confirmed to be IgG4‐related retroperitoneal fibrosis on the basis of extensive histopathological analysis. Immunosuppressive therapy resulted in a decrease in fibrosis and restoration of renal function.