Ureterosciatic herniation is an extremely rare cause of ureteral obstruction, of which few cases have been published. We describe a case revealed by pyelonephritis with acute renal failure in an 81-year-old woman. After percutaneous nephrostomy tube placement and antibiotic therapy, urography and multiplanar computed tomography reconstructions of the pelvis confirmed the diagnosis. The symptoms resolved, and the hernia was then corrected surgically.