In proven cases of segmental ulcerative colitis or segmental Crohn's colitis, roentgenograms after barium enema administration were accurate in detecting the lesion but were not completely reliable in differentiating the two conditions. Features such as sigmoid involvement, "skip lesions," stricture, or fistula are highly suggestive that the segmental colitis is due to Crohn's disease. It recurs frequently after resection, especially in younger patients. The pathologic features include gross thickening of the intestinal wall. Microscopically, there is inflammation of all coats, mucosal ulceration, and giant cell granulomas. Roentgenographically, there is evidence of mucosal ulceration, loss of haustration, irregularity of the lumen which may be narrowed, and, occasionally, strictures or fistulas. The appearance may suggest carcinoma. Involvement of the sigmoid colon or alternating normal and diseased segments in the colon are particularly suggestive of this condition. Segmental ulcerative colitis occurred in slightly older patients compared to Crohn's colitis, and results after resection were more favorable. Pathologically, there is ulceration of the mucosa, crypt abscesses, and inflammation mostly limited to the mucosa and submucosa. Roentgenographically, the colon appears shortened in the involved area with ulcerated mucosa, formation of pseudopolyps, and, often, irregularity of the process in the involved segment suggestive of carcinomatous change.