Kidney stone disease or urinary stone disease is a crystallopathy that occurs when there are too many minerals in the urine and not enough liquid or hydration. This imbalance causes tiny pieces of crystal to aggregate and form hard masses, or calculi (stones) in the upper urinary tract. Because renal calculi typically form in the kidney, if small enough, they are able to leave the urinary tract via the urine stream. A small calculus may pass without causing symptoms. However, if a stone grows to more than 5 millimeters (0.2 inches), it can cause a blockage of the ureter, resulting in extremely sharp and severe pain (renal colic) in the lower back that often radiates downward to the groin. A calculus may also result in blood in the urine, vomiting (due to severe pain), swelling of the kidney, or painful urination. About half of all people who have had a kidney stone are likely to develop another within ten years.
Renal is Latin for "kidney", while nephro is the Greek equivalent. Lithiasis (Gr.) and calculus (Lat.- pl. calculi) both mean stone.