['The risk of serious complications after colonoscopy has important implications for the overall benefits of colorectal cancer screening programs. We evaluated the incidence of serious complications within 30 days after screening or surveillance colonoscopies in diverse clinical settings and sought to identify potential risk factors for complications.', 'Patients age 40 and over undergoing colonoscopy for screening, surveillance, or evaluation based an abnormal result from another screening test were enrolled through the National Endoscopic Database (CORI). Patients completed a standardized telephone interview approximately 7 and 30 days after their colonoscopy. We estimated the incidence of serious complications within 30 days of colonoscopy and identified risk factors associated with complications using logistic regression analyses.', 'We enrolled 21,375 patients. Gastrointestinal bleeding requiring hospitalization occurred in 34 patients (incidence 1.59/1000 exams; 95% confidence interval [CI], 1.10-2.22). Perforations occurred in 4 patients (0.19/1000 exams; 95% CI, 0.05-0.48), diverticulitis requiring hospitalization in 5 patients (0.23/1000 exams; 95% CI, 0.08-0.54), and postpolypectomy syndrome in 2 patients (0.09/1000 exams; 95% CI, 0.02-0.30). The overall incidence of complications directly related to colonoscopy was 2.01 per 1000 exams (95% CI, 1.46-2.71). Two of the 4 perforations occurred without biopsy or polypectomy. The risk of complications increased with preprocedure warfarin use and performance of polypectomy with cautery.'] Are serious complications within 30 days of screening and surveillance colonoscopy uncommon?