Colonoscopy is an essential diagnostic and therapeutic tool for many gastrointestinal diseases and is also a key element in the prevention and early diagnosis of colon cancer. Despite numerous technical advances, colonoscopy continues to be uncomfortable for patients, both during and after the procedure. To a large extent, the discomfort of colonoscopy depends on the need to distend the colon, which usually produces abdominal pain. Although ambient air is usually employed to expand and inflate the colon, in the last few years devices that allow carbon dioxide (CO2) insufflation in colonoscopy have been developed. This gas is a highly attractive option for pain-free colonoscopy. (c) 2012 Elsevier Espana, S.L. and AEEH y AEG. All rights reserved.