Two patients who had undergone proctocolectomy for ulcerative colitis developed lesions in their ileal stoma that appeared to be inflammatory polyps morphologically similar to those encountered in the large intestine of ulcerative colitis patients. One of these patients eventually developed mucinous adenocarcinoma in the ileal stoma. The ileal mucosa adjacent to the neoplasm had morphologic features of large-bowel mucosa and was richly populated by sulfomucin-containing goblet cells, which are characteristic of large-bowel mucosa. Sulfomucin-containing goblet cells were also found in the inflammatory lesions biopsied from the ileal stomas of both patients, as well as from the adenocarcinoma found in one patient. These findings support the hypothesis that colonic metaplasia can occur in ileal stomas of ulcerative colitis patients. Furthermore, the metaplastic colonic tissue is the site of origin of lesions typically found in ulcerative colitis. Colonic metaplasia occurring in ileal stoma should be recognized by pathologists as a clinical entity. When colonic metaplasia is identified in the ileal stoma of an ulcerative colitis patient, biopsy surveillance of stomal mucosa is recommended.