The objective of this study was to test the hypothesis that nonparticipation in organized mammography screening is due to insufficient understanding of the information in the invitation letter by relating educational level to user pattern. Data from two Danish mammography screening programmes in Copenhagen, 1991-1999, and Funen, 1993-2001 were taken for this study. The Danish Central Population Register was used to define target groups; screened participation data were provided by the health authority, and data on highest obtained education came from Statistics Denmark. Data on all breast imaging in 2000 outside organized screening were provided by radiology clinics. Included were all women eligible for at least three screens, and participation was classified into four mutually exclusive user groups. Organized mammography screening programmes in Copenhagen and Funen, Denmark were used as field of this study. Main outcome measures were age-adjusted relative risks (RR) and 95% confidence intervals (CI) of 'never use' versus 'always use' of screening by educational level, using women with secretarial/sales education as baseline. The RR of 'never use' was 1.65 (95% CI: 1.37-1.99) in Copenhagen and 1.93 (95% CI: 1.42-2.62) in Funen for academics, 1.60 (95% CI: 1.48-1.73) in Copenhagen and 1.26 (95% CI: 1.14-1.39) Funen for women with lower primary educational level. Taking other breast imaging into account, the RR was 1.60 (95% CI: 1.32-1.95) for academics in Copenhagen, and 1.90 (95% CI: 1.75-2.07) for women with lower primary education. In conclusion, our results did not support the hypothesis that lack of understanding the information in the invitation letter explains nonparticipation. 'Never use' was not inversely associated with the level of education, but showed a U-shaped association, even when use of breast imaging outside organized screening was taken into account.