Adult megacolon can undergo colonoscopy as long as there are indications for the test and no relevant contraindications. Adult megacolon is both congenital and acquired and may present with constipation and abdominal pain. In some cases of megacolon associated with ulcerative colitis and suspected malignant organic lesions, colonoscopy can be performed to clarify the condition. In addition, for acute pseudo-colonic obstruction syndrome, enteroscopy can achieve the purpose of decompression therapy by suctioning out the intestinal gas and fluid. In cases of acute cardiopulmonary insufficiency or unstable vital signs such as shock, acute abdomen, pregnancy, narrowing or obstruction of the intestinal lumen, toxic megacolon, or during menstruation, colonoscopy is contraindicated. When megacolon occurs, it is recommended to go to the hospital promptly.