Azotemia due to urinary tract obstruction is termed postrenal azotemia. Obstruction of urinary flow from both kidneys is usually necessary for azotemia and oliguria/anuria in these conditions. Complete obstruction eventually develops into AKI and kid-ney failure, whereas prolonged partial obstruction leads to chronic renal impairment. Rapid diagnosis and relief of acute obstruction usually restore nor-mal renal function, often accompanied by a diure-sis. Obstruction may be diagnosed by a physical examination (the upper margin of the bladder can be percussed) or ultrasound (showing a distended bladder) or suggested by a radiograph of the abdo-men (revealing bilateral renal calculi), but is defini-tively diagnosed by demonstrating dilation of the urinary tract proximal to the site of obstruction on imaging studies. Treatment depends on the site of obstruction. Obstruction at the bladder outlet can be relieved with catheterization of the bladder or suprapubic cystostomy, whereas ureteral obstruc-tion requires nephrostomy or ureteral stents.