Diverting the fecal stream has been considered to affect the course of Crohn's disease favorably. Adverse effects on the distal segment have not previously been distinguished from clinical signs and symptoms. The course of four patients with Crohn's disease who underwent fecal diversion with an in situ rectum were observed in whom sigmoidoscopy was initially normal at the time of the diversion, became distinctly abnormal during the year after the diversion, and then returned to normal within 3 mo following reestablishment of intestinal continuity. The entity of nonspecific diversion proctitis might account for this phenomenon independently or by accelerating the Crohn's disease process. The inflammation present was nonspecific and did not show the stigmata of Crohn's disease. Continuity of the intestinal tract should be maintained in the course of Crohn's disease surgery if feasible. If a diversion is clinically warranted, reanastomosis should be considered as early as possible despite evidence of inflammation in the rectal mucosa.