There is no effective time for colonoscopy. The time interval for colonoscopy is different for different groups of people and different disease conditions. 1. If the patient has no growths in the intestines, no inflammatory polyps, and everything is normal, it can be done once every 5 to 10 years. 2. For patients with a single polyp in the intestine and benign pathologic examination, enteroscopy needs to be done once a year at the beginning, and the examination is normal for 2~3 consecutive years, and then it can be changed to once every 5~10 years. 3. For patients with history of colon polyps and family history, the frequency of examination should be increased, such as once a year after the age of 45. 4. For patients with postoperative colorectal cancer, colonoscopy should be done 2~3 times within one year after surgery, and then according to the examination results, decide to do colonoscopy every 3~5 years, or follow the doctor’s advice. 5. For patients with familial adenomatous polyposis, colonoscopy should be performed annually from the age of 10~12 years old to record the number and size of the polyps and to remove the polyps at an early stage. Therefore, if patients need to undergo colonoscopy, please go to the hospital as soon as possible and follow the doctor’s instructions.