Preoperative films of 176 patients operated upon for Crohn's disease were reviewed and compared with microscopic findings in the resected specimens in order to assess the accuracy of the radiographic techniques used. It was found that a diagnosis of the presence and the extent of the disease was often dependent on the demonstration of minor mucosal ulcers and less marked submucosal edema. These lesions were not adequately demonstrated by any of the techniques used for small bowel examination, but were consistently revealed by the double-contrast technique used for examination of the colon.