AIM: To assess the appropriateness of referrals and to determine the diagnostic yield of colonoscopy according to the 2000 guidelines of the American Society for Gastrointestinal Endoscopy (ASGE).METHODS: A total of 736 consecutive patients (415males, 321 females; mean age 43.6±16.6 years)undergoing colonoscopy during October 2001-March2002 Were prospectively enrolled in the study. The 2000ASGE guidelines were used to assess the appropriateness of the indications for the procedure. Diagnostic yield was defined as the ratio between significant findings detected on colonoscopy and the total number of procedures performed for that indication.RESULTS: The large majority (64%) of patients had colonoscopy for an indication that was considered"generally indicated"; it was "generally not indicated" for20%, and it was "not listed" for 16% in the guidelines.The diagnostic yield of colonoscopy was highest for the "generally indicated" (38%) followed by "not listed"(13%) and "generally not indicated" (5%) categories.In the multivariable analysis, the diagnostic yield was independently associated with the appropriateness of indication that was "generally indicated" (odds ratio=12.3) and referrals by gastroenterologist (odds ratio = 1.9).CONCLUSION: There is a high likelihood of inappropriate referrals for colonoscopy in an open-access endoscopy system. The diagnostic yield of the procedure is dependent on the appropriateness of indication and referring physicians specialty. Certain indications "not listed" in the guidelines have an intermediate diagnostic yield and further studies are required to evaluate whether they should be included in future revisions of the ASGE guidelines.