Objectives - The aim of this study was to describe the reasons for participating or not participating in organized (OD) or individual (ID) breast cancer screening. Methods - This cross-sectional self-administered questionnaire study was conducted in 2005 in six departmental breast cancer screening programs. A stratified random sample, based on participation in OS, the rural nature of the municipality of residence, and age group, was drawn in each department. Results - A total of 5,638 usable questionnaires were analyzed: 1,480 OS participants (response rate: 40.3%) and 4,158 non-participants in the screening program (response rate: 17.6%), of whom 3,537 had undergone individual screening (IS) and 621 had not undergone any screening. The vast majority of women surveyed were aware of the DO program. The second reading was one of the most frequently cited points of satisfaction among women in the DO group. The reasons given for not participating in the DO were primarily medical for women in the ID group and primarily personal for the others. Some women who discussed the DO invitation letter with their doctor were offered a mammogram other than the DO mammogram. Discussion-Conclusion - Campaigns targeting healthcare professionals and women should strengthen information about the quality of the DO program and, in particular, its added value compared to ID. (R.A.)