BACKGROUND: Few studies address the development of minor complications after screening or surveillance colonoscopy. OBJECTIVES: Our purpose was to examine in previously asymptomatic people the incidence of new symptoms after colonoscopy, risk factors for symptoms, and patients' perceptions of this examination. DESIGN: Prospective cohort study. Patients completed a standardized interview at 7 and 30 days after colonoscopy. PATIENTS: A total of 502 patients aged 40 years and older undergoing colonoscopy for colorectal cancer screening, surveillance, or follow-up of another abnormal screening test result. Patients were excluded if they had a history of inflammatory bowel disease, visible GI bleeding, or anemia. MAIN OUTCOME MEASURES: Incidence of minor complications and patient perceptions about colonoscopy. RESULTS: Minor complications occurred in 162 subjects (34%) before day 7 and in 29 subjects (6%) between day 7 and day 30, most commonly bloating (25%) and abdominal pain (11%). Six subjects had unexpected emergency department visits or hospitalizations within 30 days, including 2 with postpolypectomy bleeding. On multivariate analysis, minor complications were more common in women (odds ratio 1.78, 95% CI 1.21-2.62) and when the procedure lasted 20 minutes or longer. Bowel preparation was rated the most difficult part of the examination for 77%. Most subjects (94%) lost 2 or fewer days from normal activities for the colonoscopy itself, preparation, or recovery. CONCLUSIONS: Minor complications were common after screening and surveillance colonoscopy. The bowel preparation was the most difficult part of the examination for most patients. Most subjects lost 2 or fewer days from normal activities because of colonoscopy.