{Reference Type}: Case Reports {Title}: Effective therapy of pirfenidone in a patient with idiopathic retroperitoneal fibrosis: report of a case. {Author}: Zhao J;Zhang Z; {Journal}: Clin Rheumatol {Volume}: 42 {Issue}: 2 {Year}: Feb 2023 {Factor}: 3.65 {DOI}: 10.1007/s10067-022-06466-8 {Abstract}: Idiopathic retroperitoneal fibrosis (iRPF) is a chronic autoimmune disease characterized by fibroinflammatory tissue surrounding the abdominal aorta and iliac arteries and extending into the retroperitoneum to envelop neighboring structures. Hydronephrosis due to obstruction of ureters is the most common complication of iRPF. Glucocorticoid with or without immunosuppressants or tamoxifen, the mainstay of iRPF treatment, usually brings good response. Nevertheless, in some conditions, the obstruction of ureters remains unresolved with the treatment of all these medications. One of the reasons lies in the innate feature of the fibroinflammatory tissue. The proliferation of fibrosis tissue in addition to inflammation in the mass was associated with insufficient response to immunosuppressive therapies. Pirfenidone, an anti-fibrosis agent, has been successful in treating pulmonary fibrosis and renal fibrosis. Therefore, it is rationale to assume the effectiveness of pirfenidone in the treatment of iRPF. In the current article, we report a 61-year-old Chinese man with iRPF who responded well to pirfenidone.