Colonoscopy is an accepted technique for investigation of the colon. No portion of the large bowel is inaccessible to the diagnostic and therapeutic approach by flexible colonoscopy. The technical aspects of instrumentation have yielded to progress, with a small television chip currently incorporated into the tip of endoscopes transmitting an excellent image of the colon. Primary colonoscopy is being performed for selected indications, and, as facility with the technique increases, there will be a greater tendency for the performance of primary colonoscopy. Interruption of the adenoma-carcinoma sequence by techniques of snare-polypectomy may serve to markedly decrease the incidence of colon cancer over the next generation.