An instance is presented in which a large vesical calculus was formed from two smaller stones by a further deposition of urinary salts, and in which a mistaken diagnosis of carcinoma of the prostate was made due to the lower portion of the stone pressing on the prostate gland. This error could have been averted by a routine physical examination of the urinary system. The importance of bimanual examination is especially stressed. It is particularly useful in examining for vesical calculi.