Retroperitoneal fibrosis (RPF) is characterized by the development of peritoneal inflammation and fibrosis, which often lead to obstructive uropathy. We experienced a case of retroperitoneal fibrosis with postrenal acute kidney injury. A 50-year-old female with no past medical history presented to the emergency department for the sudden onset of difficulty in voiding that began 2 days prior. She had prolonged both flank pain and fatigue for 1 month. The physical examination findings showed that the patient had bilateral costovertebral angle tenderness. Initial laboratory data revealed a white blood cell count of 9,660 cells/μL (neutrophil 72.8%, lymphocyte 20.3%, monocyte 3.9%), a hemoglobin level of 13.7 g/dL, a platelet count of 237,000 cells/μL, a serum total protein concentration of 7.9 g/dL, an albumin concentration of 4.3 g/dL, a blood urea nitrogen level of 42 mg/dL, a serum creatinine  level of 5.74 mg/dL, and a C-reactive protein (CRP) level of 5.09 mg/dL. The patient’s urinalysis revealed no proteinuria, 1-4 white blood cells per high-power field, and 5-8 red blood cells per high-power field. Evaluation of autoimmune test showed negative findings of antinuclear antibodies (ANA), antineutrophil cytoplasmic antibodies (ANCA), and rheumatoid factor (RF). Serum level of IgG subclass-4 was within the normal range (33.0 mg/dL; normal range: 2.4-121.0 mg/dL). The three-dimensional (3D) computed tomography angiography demonstrated low density soft tissue around the lower abdominal aorta to both common iliac vessels with both ureteral occlusions (Figure 1). Prompt percutaneous nephrostomy was performed for urgent decompression. Induction therapy with high dose prednisone (1mg/kg/day) initiated. Upon discharge, bilateral nephrostomy drainage was removed and instead double-j ureteral stent was replaced. The fibrotic mass decreased in size after steroid treatment (Figure 1). The patient is fully recovered from acute kidney injury and is now in the tapering process of steroid treatment.