Kidney stones (renal lithiasis) are small, hard deposits that form inside your kidneys. Kidney stones are made of mineral and acid salts. Kidney stones have many causes. In one common scenario, kidney stones form when the urine becomes concentrated, allowing minerals to crystallize and stick together.

Passing kidney stones can be painful. The pain of a kidney stone typically starts in your side or back, just below your ribs, and moves to your lower abdomen and groin. The pain may change as the kidney stone moves through your urinary tract.

Kidney stones usually cause no permanent damage. Apart from pain medication and drinking lots of water, treatment is often unnecessary. However, treatment may help prevent recurrent kidney stones in people with increased risk.