Inflammation limited to excluded segments of the colon was observed in 10 patients without prior inflammatory bowel disease who had undergone colostomy or ileostomy for various indications. With the exception of 1 patient who complained of mucoid rectal discharge, the patients were asymptomatic when the lesion was discovered; 2 others subsequently developed mild symptoms. The proctoscopic findings were similar in appearance to those of mild ulcerative colitis. In 8 of 10 patients the inflammatory changes were confined to the distal few centimeters of the rectum, while in the remaining 2 patients the entire excluded segment was affected. Microscopic alterations were focal and included crypt abscesses, epithelial cell degeneration, acute and chronic inflammation in the lamina propria, and regenerative changes in the crypts. The inflammation persisted for as long as 8 yr in the 5 patients who did not have restoration of intestinal continuity, but subsided in the 5 patients whose colostomies were closed. The prior as subsequent clinical courses of these patients, together with the focal, nonspecific microscopic features, strongly suggest that the inflammation in these patients resulted from diversion of the fecal stream and was not a recognized form of specific or idiopathic colitis. Diversion-related colitis must not be confused with other forms of inflammation since this may result in improper therapy and/or delay in treatment of the condition for which the fecal diversion was performed.