The treatment of urinary stones is directly related to their volume. Stones smaller than 6 mm mostly need no treatment because they can pass through the urinary tract. Kidney stones smaller than 20 mm can be treated using shock wave lithotripsy. Stones larger than 20 mm in the kidney must be treated using percutaneus nephrolithotomy. Kidney stones of 15-20 mm can be treated using retrograde intrarenal surgery.