201 patients with Crohn's disease underwent air contrast examination of the colon. The Diagnosis was histologically confirmed in each case. Most of the pathological changes of Crohn's disease of the colon are manifested as alterations of the mucosal surface. These changes are excellently demonstrated by the air contrast technique. The roentgenologic findings in colonic Crohn's disease are being discussed as well as cecal deformities and rectal changes. Some conditions that may mimic colonic Crohn's disease are summarized. Finally the advantages and disadvantages with the air contrast technique are given.