Inflammatory bowel disease is a general term for two closely related conditions, ulcerative colitis and regional enteritis or Crohn's disease. The diseases can affect the colon, distal, small intestine, and sometimes other portions of the gastrointestinal tract as well as several sites outside the gastrointestinal tract. In 15–25% of cases limited to the colon, ulcerative colitis and Crohn's disease cannot be distinguished by clinical manifestations, x-ray examination, or even pathology. For this reason the broad term inflammatory bowel diseases is useful. The cause of these diseases is unknown.