Crohn's krohnz, disease, is an illness characterized by inflammation of the gastrointestinal tract (the stomach and intestines). The disease usually affects the lower part of the small intestine, called the ileum, and parts of the large intestine. The disease is also called ileitis, regional enteritis, or granulomatous colitis, depending upon the location of the inflammation. Crohn's disease is similar to ulcerative colitis, and together they are referred to as inflammatory bowel disease. See Inflammatory bowel disease.