May also be called: Calculi; Nephrolithiasis Kidney stones are small, solid masses that form in the urinary tract. Kidney stones are caused by the build-up of substances normally found in urine (pee), like salts and calcium. More to Know When substances normally found in urine become extra concentrated, they can form crystals in the kidneys. These crystals can build up to become stones over a few weeks or months. Small kidney stones can pass through the urinary tract and out of the body with little or no pain, but larger stones can be quite painful, block the flow of urine, and cause blood in the urine and other symptoms. In some cases, kidney stones can lead to problems with the kidneys and urinary tract. Most kidney stones, however, cause no permanent damage. Keep in Mind Kidney stones are fairly common. There are different types of kidney stones with many different causes. Treatment depends on the type and size of the stones. All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts. Back to Articles Related Articles A to Z: Hematuria (Blood in Urine) Learn more about hematuria (blood in urine) and how it's treated. Read More A to Z: Glomerulonephritis Glomerulonephritis is an inflammation of the glomeruli, the parts of the filtering units (nephrons) of the kidney. Read More A to Z: Hyperkalemia Learn more about diseases and conditions of the blood and kidneys. Read More Glomerulonephritis With glomerulonephritis, tiny filtering units in the kidneys stop working properly, causing problems like too much fluid in the body and swelling. Most of the time it can be treated. Find out more. Read More Kidney Disease Sometimes, the kidneys can't do their job properly. In teens, kidney disease is usually due to infections, structural issues, glomerulonephritis, or nephrotic syndrome. Read More Kidney Diseases in Childhood The kidneys play a critical role in health. When something goes wrong, it could indicate a kidney disease. What are kidney diseases, and how can they be treated? Read More Kidneys and Urinary Tract The kidneys perform several functions that are essential to health, the most important of which are to filter blood and produce urine. Read More Your Kidneys You need at least one kidney to live. Find out why in this article for kids. Read More Kidney Stones Kidney stones mostly happen to adults, but sometimes teens can get them. Find out what kidney stones are, how to treat them, and ways to help prevent them. Read More Kidneys and Urinary Tract The bean-shaped kidneys, each about the size of a child's fist, are essential to our health. Their most important role is to filter blood and produce urine. Read More Urine Test: 24-Hour Analysis for Kidney Stones This test can show if certain substances are found at high concentrations in the urine, and might be causing kidney stones. Read More Ultrasound: Renal (Kidneys, Ureters, Bladder) A renal ultrasound makes images of your child's kidneys, ureters, and bladder. Doctors may order this test if they suspect kidney damage, cysts, tumors, kidney stones, or complications from urinary tract infections. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.