SummaryBackgroundColonoscopy is frequently performed in industrialised countries. Inappropriate colonoscopies might lead to unnecessary exams, increasing risks and costs.AimTo estimate the impact of colonoscopy appropriateness in terms of gain in additional diagnoses and sparing of unnecessary exams.MethodsSystematic review including studies reporting the prevalence of relevant findings, colorectal cancer (CRC) and inflammatory bowel disease (IBD) according to colonoscopy appropriateness as defined by the American Society for Gastrointestinal Endoscopy and European Panel on Appropriateness of Gastrointestinal Endoscopy.ResultsTwenty‐one studies with 19,822 patients were included. Colonoscopy was appropriate in 15,162 (71%, CI 64%‐78%). Appropriateness significantly increased the probability of relevant findings (34% vs. 18%; RR 1.81, CI 1.53‐2.14), CRC (7% vs. 2%; RR 3.62, CI 2.44‐5.37) and IBD (6% vs. 4%; RR 1.86, CI 1.09‐3.19). Appropriateness had sensitivity 88% (CI 85%‐91%), 97% (CI 93%‐98%) and 89% (CI 80%‐94%), and specificity 24% (CI 20%‐29%), 22% (CI 18%‐26%) and 24% (CI 20%‐28%) for relevant findings, CRC and IBD, respectively. On average, performing colonoscopy with appropriate indication would find 15 (CI 10‐21) more relevant findings, five (CI 3‐9) more CRCs and three (CI 1‐9) more diagnoses of IBD per 100 patients, and save 24 (CI 20‐29), 22 (CI 18‐26) and 24 (CI 20‐28) examinations per 100 patients for relevant findings, CRC and IBD, respectively.ConclusionsAppropriateness affects the diagnostic yield of colonoscopy for CRC, IBD and relevant findings. Appropriateness criteria are useful, although integrated with clinical evaluation of the patient.