There are several methods of contrast administration when performing computed tomography (CT) scanning for suspected appendicitis. In this systematic review we evaluated the diagnostic performance of CT with and without contrast material. Twenty-three reports were identified using a Medline search. The aggregated diagnostic performance characteristics of all modes of CT scanning were excellent with a range of sensitivity (83–97%), specificity (93–98%), positive predictive value (86–98%), negative predictive value (94–99%), and accuracy (92–97%). The diagnostic performance of CT without oral contrast was similar (sensitivity, 95% vs. 92% not statistically significant; negative predictive value, 96% for both protocols) or surprisingly better (specificity, 97% vs. 94%; positive predictive value, 97% vs. 89%; accuracy, 96% vs. 92%; P < .0001) than with oral contrast. Noncontrast CT techniques to diagnose appendicitis showed equivalent or better diagnostic performance compared with CT scanning with oral contrast. A prospective comparative trial of CT with and without oral contrast for appendicitis should be performed to assess the adequacy of this modality.