Colonoscopy (fiberoptic colon or e-colonoscopy) is usually required in the following cases: 1. When there is blood in the stool or dark red blood in the stool and the location of the lesion is considered to be in the colon or rectum. 2, repeated diarrhea, constipation or stool with pus and blood. 3, when there is unexplained abdominal pain, anemia or body wasting. 4.When there is a sudden change in stool habit or difficulty in defecation. 5.When abnormalities are found in gas-barium enema or gastrointestinal imaging and further examination of the colon or aspiration is needed to confirm the nature of the lesion. 6.Colon lesions have been found, when considering treatment by colonoscopy. 7.After the treatment of colorectal polyps or tumors, when the review. 8.Screening of colorectal tumors, especially for those with high incidence of colorectal cancer, elderly people and family history of colorectal tumors. 9.When there is a high suspicion of schistosomiasis and the stool examination is negative for several times.