Who usually performs colonoscopies, gastroenterologists or colon and rectal surgeons?

Both: Depends on whose available within your community.

Both: Both do however if a mass is there the colon and rectal surgeon can take care of it. In addition a colorectal surgeon would be more agressive at removing a polyp whereas a GI may be more apt to recommend surgery. This is based on personal experience. Fyi colonoscopy was pioneered by a general and cardiothoracic surgeon at beth israel in ny. Dr wolff and dr shinya invented polypectomy.

Both: Both perform colonoscopies. Gastroenterologists typically perform more on average.