For stones less than one inch in size in the kidney or for many stones that drop into the ureter, shock wave lithotripsy (SWL) can be very effective treatment. This procedure uses shock waves that are produced by a machine outside the body. Using x-ray or ultrasound, the shock waves are focused on the stone inside the kidney or ureter to break it into sand or gravel, which is then passed out in the urine. This procedure can be performed as an outpatient procedure and the patient can usually return to regular activities or work within a few days of the treatment. Blood in the urine for several days after the SWL is normal. Blockage of urine flow from the kidney can occur in less than 10% of patients, while the stone fragments pass. If this causes severe pain or blockage of the kidney, a tube may be placed through the back into the kidney to keep it drained until the fragments all pass out of the ureter.