Bladder stones. Coloured urogram X-ray of the abdomen of a 33 year old male patient, showing five large stones in the bladder. At lower centre the stones (pink) are surrounded by the hip bones. At upper left and right are tree-shaped renal pelvises of each kidney from which two ureters pass urine down to the bladder. Bladder stones are crystalline masses caused by precipitation of salts in the urine. Urinary stone disease (uro- lithiasis) is usually the result of a diet low in phosphate & protein, or a urinary tract infection. Large stones such as these usually require surgical removal.