I. What is colonoscopy? Colonoscopy is an examination method of inserting a colonoscope through the anus to the ileocecal part of the colon and observing the colonic lesions from the mucosal side. It is the best method to diagnose colonic mucosal lesions at present. Under what circumstances should colonoscopy be performed? (1) those who have obvious changes in stool habits: increased number of stools, mucus stools and other abnormalities; (2) those with unexplained lower gastrointestinal bleeding; (3) those who have been diagnosed with inflammatory bowel disease and need to clarify the distribution of lesions and early detection of malignant lesions; (4) those who have been diagnosed with colon cancer and need to further check whether there are polyps or cancerous tumors in other parts; (5) regular follow-up after colon cancer surgery and polypectomy, and regular follow-up of certain precancerous lesions (6) For people over 40 years old, colonoscopy should be performed if conditions permit; (7) If there is a family history of colorectal cancer, or live in areas with a high incidence of colorectal cancer, such as schistosomiasis infected areas, etc.