Kidney stones are caused by the accumulation of certain solid materials in the kidney. Although kidney stones can sometimes occur without causing any symptoms, many patients experience severe pain and other problems when the stone is passed in the urine. The problems may include bleeding and damage to the kidney. People who have had a kidney stone are at risk for having another, so effective measures to prevent recurrent kidney stones would be useful. Although dietary or drug therapies are often recommended, whether these therapies can prevent repeated episodes of kidney stones is not clear. In addition, doctors often perform tests to figure out what material the stones are made of to try to better direct therapy and prevent future stones. Whether this is useful is also not clear.