Bladder stones can either form in the kidneys or ureter and travel to the bladder, or form in the bladder itself. In the latter case, stones usually develop when the bladder does not completely empty urine. If urine sits in the bladder for a long enough time, minerals in the urine start to crystalize and develop into bladder stones.
Other possible causes of bladder stones include recurrent inflammation of the urinary tract and a diet high in foods that cause stones (e.g. asparagus, certain leafy vegetables, and offal), as well as not drinking enough water.
Bladder stones are much more common in men than in women. This is because the male urinary tract is longer than the female urinary tract, which means urinary sediment can remain in the urinary tract more easily.