Kidney stones are small, hard rocks which are made within the kidneys.
Sometimes kidney stones cause no symptoms. When kidney stones are large or there is more than one, they may block the flow of urine. In all people, not drinking enough water or other fluids may also contribute to forming stones. Inadequate fluid intake causes the kidneys to produce less urine, as well as urine that is highly concentrated. The smaller the daily volume of urine, the more likely it is that a person would form kidney stones.