Urinary tract symptoms and signs may result from secondary involvement of the urinary bladder in patients with Crohn's disease. In a small but significant proportion of these individuals, urinary tract symptoms represent the initial or predominant mode of presentation. Such patients may be erroneously treated for primary infection of the lower urinary tract for prolonged periods before the intestinal origin of the disease process is discovered. Roentgenologic abnormalities of the urinary bladder may provide early and important clues to the correct DIAGNOSIS. The various abnormalities of the urinary bladder which may occur secondary to Crohn's disease are described and illustrated, and the roentgenologic differential diagnosis is discussed.