Retroperitoneal fibrosis (RPF) is a rare disease characterized by the presence of retroperitoneal tissue marked by chronic inflammation and prominent fibrosis. A 67-year-old man presented with general weakness and oliguria. Laboratory findings showed blood urea nitrogen 77.7 mg/dL, serum creatinine 9.24 mg/dL, and an IgG4 level within the normal range. Computed tomography (CT) findings showed bilateral hydronephrosis and distal ureteral obstruction due to fibrotic adhesion to a presacral mass. Laparoscopic biopsy was performed. The authors report a case of acute kidney injury caused by non-IgG4 related focal retroperitoneal fibrosis in the pelvis that was successfully treated using prednisolone and tamoxifen… non-IgG4 related focal retroperitoneal fibrosis caused byacute kidney injury.