OBJECTIVE : Patients with a chronic comorbidity or multiple comorbidities are at much greater risk of serious colonoscopy-related gastrointestinal (GI) adverse events relative to patients with no comorbidity. It is important to identify outpatient facilities that can effectively and safely provide colonoscopy to complex patients. To address this need, the association between outpatient facilities' complex care volume and type (ambulatory surgery center (ASC) and hospital outpatient department (HOPD)) and the risks of serious GI adverse events in colonoscopy patients with single and multiple chronic comorbidities were examined. METHODS : Outpatient colonoscopies of 1,020,372 patients with single and multiple comorbidities were investigated, using a retrospective cohort study. Thirty-day hospitalizations due to colonic perforations and GI bleeding were examined. Ambulatory surgery and hospital discharge datasets from California, Florida, and New York for 2006-2009 were used. RESULTS : Higher complex care volume was associated with lower risks of adverse events in patients with comorbidities (OR 1.69; 95% CI [1.13, 2.54]). ASCs had higher risks of adverse events in patients with comorbidities relative to HOPDs (OR 2.85; 95% CI [2.40, 3.38]). Patients with single and multiple comorbid conditions, patients with systemic diseases, and complex patients of advanced age had higher risks of adverse events. CONCLUSIONS : Referring patients with single and multiple chronic comorbidities to facilities experienced in treating complex patients, or HOPDs, may reduce colonoscopy-related adverse events.