A gastroenterologist is the best doctor to perform a colonoscopy. Gastroenterologists are specialists in gastrointestinal diseases and have received special training in colonoscopy. They perform more colonoscopies by far than any other specialty, and non-gastroenterologists are five times more likely to miss colorectal cancer during colonoscopy than gastroenterologists. Colorectal surgeons are also specialists in performing colonoscopies and are more likely to detect when there may be cancer present. However, it is still better to have a colonoscopy performed by a non-gastroenterologist than not having one at all.