A small, hard object that forms in the kidney and is often painful when passed.

A kidney stone is made of minerals and salts from the urine. Often, a stone forms when the urine has less water in it. This lets minerals form crystals and stick together. Kidney stone causes can include diet, extra body weight, some health conditions, and some supplements and medicines.

Kidney stone symptoms may not start until the stone moves around in the kidney or passes into one of the tubes that connect the kidneys to the bladder. A stone stuck in one of the tubes can cause sharp pain in the side and back, below the ribs.

Kidney stone treatment often includes taking pain relievers and drinking water. Other treatments may be needed to remove or break up larger stones. Diet changes and medicine can help prevent more kidney stones.