Kidney stones are deposits in the urinary tract or kidneys made from substances in the urine. They are crystals that are usually dissolved in urine and excreted. If there are too many crystals, they form stones, which are then deposited in the kidneys, urinary tract or bladder. They can move about, and get stuck or infected. Kidney stones are often passed of their own accord. Treatment of larger stones may involve the stones being broken up mechanically or using drugs. The indicator shows the frequency of inpatient treatments as a result of kidney stones, both when it is coded as the principal diagnosis and when it is coded as principal or secondary diagnosis.