BACKGROUND: The rate of serious complications is one marker of the quality of colonoscopy services.OBJECTIVE: To estimate the rate of serious complications of colonoscopy according to colonoscopy indication and polypectomy status.METHODS: A prospective cohort study of patients scheduled for colonoscopy who were recruited from seven endoscopy facilities across Montreal (Quebec) was conducted. Before colonoscopy, patients completed a brief questionnaire and provided their health insurance numbers. Colonoscopy indication was based on patient-reported medical history. Polypectomy status was obtained from provincial physician billing records (Régie de l’assurance maladie du Québec). Diagnoses and procedures associated with hospitalization in the 30 days following colonoscopy were obtained from the provincial hospitalization database (MedEcho).RESULTS: Of the 2134 patients enrolled (mean age 60.9 years, 50.1% male), 33 (1.55% [95% CI 1.06% to 2.16%]) were hospitalized within 30 days. One patient experienced bleeding following a colonoscopy that involved polypectomy and was diagnosed with carcinoma in situ of the rectum. Based on self-reported rectal bleeding in the previous six months, the colonoscopy was nonscreening. The provincial hospitalization data showed no occurrences of perforation, diverticulitis, myocardial infarction/stroke or death; thus, the rate of serious colonoscopy complications was 0.05% (95% CI 0.00% to 0.26%).DISCUSSION: The rate of serious colonoscopy complications requiring hospitalization was low and comparable with what is reported in the literature. The serious complication occurred subsequent to polypectomy and in a nonscreening colonoscopy.CONCLUSION: The findings support the relative safety of screening colonoscopy in persons without large bowel diseases and symptoms. However, future research to determine the rate of serious complications not requiring hospitalization is warranted to reassure decision makers of the safety of colonoscopy for colorectal cancer screening.