AIM:To assess whether in ulcerative colitis (UC) patients with ileo-rectal anastomosis (IRA),ileal lesions may develop in the neo-terminal-ileum and their possible relation with phenotypic changes towards colonic epithelium.METHODS:A total of 19 patients with IRA under regular follow up were enrolled,including 11.UC and 8 controls (6 Crohn's disease,CD;1 familial adenomatous polyposis,FAP;1 colon cancer,colon K).Ileal lesions were identified by ileoscopy with biopsies taken from the ileum (involved and uninvolved) and from the rectal stump.Staining included HE and immunohistochemistry using monoclonal antibodies against colonic epithelial protein CEP (Das-1) and human tropomyosin isoform 5,hTMS (CG3).Possible relation between development of colonic metaplasia and ileal lesions was investigated.RESULTS:Stenosing adenocarcinoma of the rectal stump was detected in 1 UC patient.The neo-terminal ileum was therefore investigated in 10/11 UC patients.Ileal ulcers were detected in 7/10 UC,associated with colonic metaplasia in 4/7 (57.1%) and Das-1 and CG3 reactivity in 3/4 UC.In controls,recurrence occurred in 4/6 CD,associated with colonic metaplasia in 3/4 and reactivity with Das-1 and CG3 in 2/3.CONCLUSION:Present findings suggest that in UC,ileal lesions associated with changes towards colonic epithelium may develop also after IRA.Changes of the ileal content after colectomy may contribute to the development of colonic metaplasia,leading to ileal lesions both in the pouch and in the neo-terminal ileum after IRA.