Kidney stone, urolithiasis, lithiasis disease. Kidney stone is a condition that affects the kidney shown in blue. These are small pebbles (in red) of variable size which are produced by the kidneys at the level of the renal cavities. They can remain in the cavities. We see two at the level of the chalices on this drawing. Or they can migrate along the ureter. In 70% of cases, kidney stones are eliminated in the urine. But in some cases, they can get stuck in the ureter as illustrated in this drawing at the bottom left and trigger nephritic colic.