Colonoscopy (fiberoptic colonoscopy 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.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 clarification of the nature of the lesion is needed. 6.Colon lesions have been found, when considering treatment by colonoscopy. 7.After the treatment of colorectal polyps or tumors, when re-examining. 8.Censuses of colorectal tumors, especially for those in areas with high incidence of colorectal cancer, the elderly, and those with family history of colorectal tumors. 9.Highly suspect schistosomiasis, and when the stool examination is negative for several times.