The main job of the kidneys is to remove wastes from the blood and return the cleaned blood back to the body. The ureters carry the waste products, as urine, from the kidneys to the bladder where it is stored until you urinate. A kidney stone can develop when certain chemicals in your urine form crystals that stick together. The crystals may grow into a stone ranging in size from a grain of sand to a golf ball. Small stones can pass through the urinary system without causing problems.
Most stones form in the kidney.
Kidney stones occur much more commonly in men than in women. Normally, urine contains chemicals which prevent crystals from forming. However, this does not work for some people who seem to be more prone to stones than others. Severe pain that usually starts suddenly in the small of the back under the ribs or in the lower abdomen, and may move to the groin. An X-ray of the kidneys, ureters and bladder can reveal the presence of most stones.