Inflammatory bowel disease refers to two different but related diseases. Ulcerative colitis and Crohns disease are incurable chronic diseases of the intestinal tract. The two diseases are often grouped together as inflammatory bowel disease (IBD) because of their similar symptoms. As many as four million people (including one million Americans, 23,000 Australians, and 250,000 Canadians) worldwide suffer from a form IBD. Crohns disease can affect the small and large intestine as well as other organs in the digestive tract. Unlike ulcerative colitis, which only affects the inner layer, Crohns disease commonly involves all layers of the intestinal wall. Ulcerative colitis, affects the inner lining of the large intestine (colon) and rectum. The disease does not affect the small intestine.