Rectal prolapse is a protrusion of the rectum beyond the anal canal. Since rectal prolapse is a surgical disease, it is mostly diagnosed and treated at the surgical department. However, when surgical complications occur or they are suspected after an operation for colorectal disease, colonoscopy may now have a role in diagnosing the actual status of the problem. We present here the case of penetration of mesh at the distal rectum that was incidentally diagnosed by colonoscopy and the patient had previously undergone presacral rectopexy for rectal prolapse. Only one such case has been reported abroad and there has been no such case report in Korea. We report here on a case for which colonoscopy had a crucial role in diagnosing an occult complication after a colorectal operation that used a prosthesis.