Gastrointestinal bleeding is when bleeding occurs in the digestive tract. It is also called GI bleeding. Bleeding can be anywhere from the mouth to the anus. The anus is the opening where stool leaves the body. GI bleeding is most often a sign of some other health problem. It is often hard to find the cause. When it happens in the upper digestive tract it is called upper GI bleeding. The stool can be very dark, almost black in color, and tarry. When it is in the lower digestive tract it is called lower GI bleeding. The stool is most often red in color. There may be very little blood or a lot of blood. GI bleeding may be very serious. You may need to have a colonoscopy, endoscopy, or surgery to stop the bleeding.