Objective. There are few prospective studies of the prevalence of colonic neoplasia in the normal population. In order to properly evaluate screening-protocols for colorectal cancer in risk groups (e.g., older subjects or those with a family history), it is essential to know the prevalence of adenomas and cancer in the normal population. Methods. A prospective population-based colonoscopy study on 745 individuals born in Sweden aged 1970 years was conducted (mean age 51.1 years). All polyps seen were retrieved and examined. Results. Out of the 745 individuals 27% had polyps, regardless of kind. Adenomas were found in 10% of the individuals and finding of adenomas was positively correlated to higher age. Men had adenomas in 15% and women in 6% of the cases. Women had a right-sided dominance of adenomas. Hyperplastic polyps were seen in 21% of the individuals. The presence of hyperplastic polyps was significantly positively correlated to the presence of adenomas. Advanced adenomas were seen in 2.8% of the study participants, but no cancers were detected. Conclusion. One in 10 healthy subjects had an adenoma but advanced adenomas were uncommon. Men and women have a different adenoma prevalence and localization. The results provide baseline European data for evaluating colonoscopy screening-protocols for colorectal cancer risk groups, and the findings may have implications for colon cancer screening in the normal, otherwise-healthy population.