DefinitionA kidney stone is a solid mass made up of tiny crystals. One or more stones can be in the kidney or ureter at the same time.See also: CystinuriaAlternative NamesRenal calculi; Nephrolithiasis; Stones - kidneyCauses, incidence, and risk factorsKidney stones can form when urine contains too much of certain substances. These substances can create small crystals that become stones.The biggest risk factor for kidney stones is dehydration.Kidney stones may not produce symptoms until they begin to move down the tubes (ureters) through which urine empties into the bladder. When this happens, the stones can block the flow of urine out of the kidneys. This causes swelling of the kidney or kidneys, causing pain. The pain is usually severe.Kidney stones are common. A person who has had kidne