http://digestive.niddk.nih.gov/ddiseases/pubs/crohns/
National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health
Crohn's disease usually involves the small intestine, most often the lower part (the ileum). In some cases, both the small and large intestine (colon or bowel) are affected. In other cases, only the colon is involved. Sometimes, inflammation also may affect the mouth, esophagus, stomach, duodenum, appendix, or anus. Crohn's disease is a chronic condition and may recur at various times over a lifetime.