Bacteriological and clinical studies of patients with acute retional ileitis indicate that numerous patients with this diagnosis have a benign ileitis of short duration, caused by Yersinia enterocolitica, whereas others develop chronic Crohn's disease. Yersinia ileitis has some clinical and radiological features in common with Crohn's disease, but the two conditions are basically separate. In Yersinia ileitis, three stages are apparent: (a) the nodular stage, lasting up to three weeks; (b) the edematous stage (4th-5th week); and (c) resolution, observed during the 5th-8th week. The radiological findings in 25 patients with Yersinia ileitis and their distinction from Crohn's disease are described.