Background: Sedation causes most of the complications of colonoscopy. Sedation is used selectively in some countries but is routine in the United States. Methods: Cross-sectional survey and randomized controlled trial were used to identify patient factors associated with willingness to try colonoscopy without sedation and to compare pain and satisfaction scores and willingness to return to the same physician in patients randomized to receive routine sedation versus as needed sedation. A single colonoscopist invited 250 consecutive eligible outpatients to be randomized to routine sedation versus as needed sedation. Seventeen who preferred no sedation and 163 who preferred sedation refused. Seventy accepted and were randomized. Results: Male gender (odds ratio 4.33; 95% CI [2.27, 8.26]), increasing age (odds ratio for 10-year increase 1.28; 95% CI [1.01, 1.06]), and absence of abdominal pain (odds ratio 5.13; 95% CI [1.68, 15.63]) were associated with willingness to be randomized. Total colonoscopy was achieved without sedation in 94% of those who received sedation only as needed. Pain scores were higher in the sedation as needed arm. All 35 patients in the routine sedation arm were “very satisfied”. In the sedation as needed arm, 31 of the 34 were “very satisfied” and 3 were “somewhat satisfied”. All randomized patients said they would return to the same colonoscopist. Patients in the sedation as needed arm had less decline in blood pressure, less hypoxemia, and lower charges than those in the routine sedation arm. Conclusions: Experienced colonoscopists should consider offering colonoscopy without sedation to selected patients. (Gastrointest Endosc 1999;49:554-9.)