A kidney stone is a solid piece of material that forms in the kidney from substances in the urine. It may be as small as a grain of sand or as large as a pearl. Most kidney stones pass out of the body without help from a doctor. But sometimes a stone will not go away. It may get stuck in the urinary tract, block the flow of urine and cause great pain.

The following may be signs of kidney stones that need a doctor's help:

• Extreme pain in your back or side that will not go away
• Blood in your urine
• Fever and chills
• Vomiting
• Urine that smells bad or looks cloudy
• A burning feeling when you urinate