Plain abdominal radiographs are helpful in patients with suspected obstruction, perforation (look for free air), or to follow previously identified stones in renal colic patients. Ultrasonography is useful for the diagnosis of cholelithiasis, choledocholithiasis, cholecystitis, biliary duct dilatation, pancreatic masses, hydroureter, intrauterine or ectopic pregnancies, ovarian and tubal pathologies, free intraperitoneal fluid, suspected appendicitis (institution specific), and abdominal aortic aneurysm. Computed tomography (CT) is the preferred imaging method for mesenteric ischemia, pancreatitis, biliary obstruction, aortic aneurysm, appendicitis, and urolithiasis and is superior for identifying virtually any abnormality that can be seen on plain films. Intravenous contrast is essential to identify vascular lesions, is helpful to identify inflammatory conditions (ie, appendicitis), but is not needed for urolithiasis. Oral contrast aids in the diagnosis of bowel obstruction, but otherwise is less useful.