OBJECTIVE: To examine the appropriateness and necessity of colonoscopy across Europe. DESIGN: Prospective observational study. SETTING: A total of 21 gastrointestinal centers from 11 countries. PARTICIPANTS: Consecutive patients referred for colonoscopy at each center. INTERVENTION: Appropriateness criteria developed by the European Panel on the Appropriateness of Gastrointestinal Endoscopy, using the RAND appropriateness method, were used to assess the appropriateness of colonoscopy. MAIN OUTCOMME MEASURE: Appropriateness of colonoscopy. RESULTS: A total of 5213 of 6004 (86.8%) patients who underwent diagnostic colonoscopy and had an appropriateness rating were included in this study. According to the criteria, 20, 26, 27, or 27% of colonoscopies were judged to be necessary, appropriate, uncertain, or inappropriate, respectively. Older patients and those with a major illness were more likely to have an appropriate or necessary indication for colonoscopy as compared to healthy patients or patients who were 45-54 years old. As compared to screening patients, patients who underwent colonoscopy for iron-deficiency anemia [OR: 30.84, 95% CI: 19.79-48.06] or change in bowel habits [OR: 3.69, 95% CI: 2.74-4.96] were more likely to have an appropriate or necessary indication, whereas patients who underwent colonoscopy for abdominal pain [OR: 0.64, 95% CI: 0.49-0.83] or chronic diarrhea [OR: 0.54, 95% CI: 0.40-0.75] were less likely to have an appropriate or necessary indication. CONCLUSIONS: This study identified significant proportions of inappropriate colonoscopies. Prospective use of the criteria by physicians referring for or performing colonoscopies may improve appropriateness and quality of care, especially in younger patients and in patients with nonspecific symptoms.