Infectious diarrhea is common in cases of ulcerative colitis (UC), caused by resistance to treatment. In particular, it has been associated with cytomegalovirus or infection has rarely been observed in human beings, but has never been seen in immunocompetent patients. We report a case of intestinal infection presenting as acute diarrhea in a patient with a 10-year history of UC who was never treated with immunosuppressants.