A kidney stone results when the urine becomes too concentrated and substances in the urine crystallize to form stones. Stones may not produce symptoms until they begin to move down the ureter, causing pain. Kidney stones are common. Kidney stones affect about 2 out of every 1,000 people. Recurrence is common, and the risk of recurrence is greater if two or more episodes of kidney stones occur.
Kidney stones are common in premature infants.
Some types of stones tend to run in families. Some types may be associated with other conditions such as bowel disease, ileal bypass for obesity , or renal tubule defects. A personal or family history of stones is associated with increased risk of stone formation. Other risk factors include renal tubular acidosis and resultant nephrocalcinosis . They are two to three times more common in men, usually appearing at age 20 to 30.