Cystinuria is an inherited metabolic disorder characterized by excessive amounts of undissolved cystine in the urine, as well as three chemically similar amino acids: arginine, lysine, and ornithine. Excess cystine in the urine can lead to the formation of crystals and stones (calculi) in the kidney, bladder, and/or urinary tract (ureters). Some people with cystinuria do not form stones, while others frequently form stones.