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A 41-year old male patient was admitted to our hospital with the complaints of reduced urine, swelling and increased urea and creatinine values. Bilateral hydronephrosis was detected by ultrasonography, but the surrounding tissues couldn’t be clearly examined. Ureteral catheter and then bilateral percutaneous nephrostomy were applied. The patient’s complaints reduced in the follow-up period. The intravenous urogram was performed to explain the reason of hydronephrosis. The left kidney was nonfunctioned while the right kidney was functioning. An abdominal computed tomography scan showed a soft-tissue mass encasing the aorta, the left ureter and left surrenal gland and causing hydronephrosis. The appearance observed by magnetic resonance imaging scan was considered consistent with the diagnosis of retroperitoneal fibrosis. The entire body Ga-67 scintigraphy demonstrated an uptake in the same area. Steroid treatment was started to the patient. A clinical recovery was observed during the follow-up period. Regression in retroperitoneal fibrosis was confirmed by the post-therapy abdominopelvic computed tomography scan and Ga-67 scintigraphy. In addition to malignancies, retroperitoneal fibrosis should be considered in the differential diagnosis of an abdominal mass observed in case with acute renal failure secondary to obstructive nephropathy.