A 15-year-old girl who presented with signs of acute infectious gastroenteritis, just as two members of her family is described. As the patient did not improve, a sigmoidoscopy was performed and the diagnosis of ulcerative colitis (UC) was made. Our hypothesis is that an infection triggered the development of UC. Her paralytic ileus was probably triggered by the increased nitric oxide produced in the macrophages and smooth muscles of the inflamed bowel.