Kidney stones form when there’s too much of a certain substance (like calcium) in your urine. They can stay in your kidney or travel down the urinary tract, where you’d pee it out.
Kidney stones are different shapes and sizes. As painful as they can be to pass, the stones can be as tiny as a grain of sand or as big as a pearl — or rarely a golf ball. You may be more likely to get a kidney stone if other people in your family have had them.