A recurrent inflammatory disease affecting the gastrointestinal tract. Sections of the intestinal tract most commonly affected include the lower part of the small intestine (ileum) and the large intestine (colon); however, any part of the digestive tract, from mouth to rectum, may be involved. It is an autoimmune disease and is most common in people between the ages of 15 and 35. Other risk factors are a family history of Crohn's disease, Jewish ancestry and smoking.