Ulcerative colitis (UC) is a chronic inflammatory disease. It affects the lining of your large intestine, or colon, and rectum. The rectum is the last section of the colon and is located just above the anus. People with ulcerative colitis have tiny ulcers and abscesses in their colon and rectum. These flare up every now and then and cause bloody stools and diarrhea. UC may also cause severe abdominal pain and low levels of healthy red blood cells, also called anemia.