AIM:To assess the prevalence and location of ad-vanced neoplasia in patients undergoing colonoscopy,and to compare the yield per indication.METHODS:In a multicenter colonoscopy survey (n = 18 hospitals) in the Amsterdam area (Northern Holland),data of all colonoscopies performed during a three month period in 2005 were analyzed. The location and the histological features of all colonic neoplasia were recorded. The prevalence and the distribution ofadvanced colorectal neoplasia and differences in yield between indication clusters were evaluated. Advanced neoplasm was defi ned as adenoma > 10 mm in size,with > 25% villous features or with high-grade dyspla-sia or cancer.RESULTS:A total of 4623 eligible patients underwent a total colonoscopy. The prevalence of advanced neo-plasia was 13%,with 281 (6%) adenocarcinomas and 342 (7%) advanced adenomas. Sixty-seven percent and 33% of advanced neoplasia were located in the distal and proximal colon,respectively. Of all patients with right-sided advanced neoplasia (n = 228),51% had a normal distal colon,whereas 27% had a syn-chronous distal adenoma. Ten percent of all colono-scopies were performed in asymptomatic patients,7% of whom had advanced neoplasia. In the respective procedure indication clusters,the prevalence of right-sided advanced neoplasia ranged from 11%-57%. CONCLUSION:One out of every 7-8 colonoscopies yielded an advanced colorectal neoplasm. Colonoscopy is warranted for the evaluation of both symptomatic and asymptomatic patients. AIM:To assess the prevalence and location of ad-vanced neoplasia in patients undergoing colonoscopy, and to compare the yield per indication.METHODS:In a multicenter colonoscopy survey (n = 18 hospitals) in the Amsterdam area (Northern Holland),data of All colonoscopies performed during a three month period in 2005 were analyzed. The location and the histological features of all colonic neoplasia were recorded. The prevalence and the distribution ofadvanced colorectal neoplasia and differences in yield between indication clusters were evaluated. Advanced neoplasm was defi ned as. Adenoma > 10 mm in size,with >25% villous features or with high-grade dyspla-sia or cancer.RESULTS:A total of 4623 eligible patients underwent a total colonoscopy. The prevalence of advanced neo-plasia was 13%,with 281 (6%) adenocarcinomas and 342 (7%) advanced adenomas. Sixty-seven percent and 33% of advanced neoplasia were located in the distal and proximal colon, respectfully. Of all patients with right-sided Advanced neoplasia (n = 228), 51% had a normal distal colon, whereas 27% had a syn-chronous distal adenoma. Ten percent of all colono-scopies were performed in asymptomatic patients, 7% of who had advanced neoplasia. In the Conclusions: One out of every 7-8 colonoscopies yielded an advanced colorectal neoplasm. Colonoscopy is warranted for the evaluation of both symptomatic and asymptomatic patients.