Objective: To understand low uptake of breast cancer screening through exploring the personal reasoning underlying women's attendance or non-attendance, and identifying differences between those who attend and those who decline. Design: Cross-sectional survey. Setting: Community and home environments of women eligible for breast screening aged 50-64 years, living in South East London. Method: Structured, self-completed or assisted-completion questionnaires. Results: The decision to attend or decline screening is rational and personally justifiable, engaging factors linked to emotions and attitude. Attitudes about breast screening and perceived personal importance of breast screening are the strongest predictors of attendance and non-attendance. There are differences between ethnic groups in perceptions of breast screening. Regular attendance at screening is associated with ethnicity, although consistent avoidance of mammography is not. Inconvenience is an important factor in missing appointments, and tends to be prolonged rather than specific to the time or day of the pre-booked invitation. GP and health worker advice are good persuaders towards attendance. Pain and anxiety during mammography are notable dissuaders against re-attending. Conclusion: Appropriate service provision requires consideration of local factors, as well as the medical needs of the population eligible for breast screening. Lay perceptions of potential personal costs of attending or not attending breast screening are important for guiding health promotion. Information providers should consider the language needs of a culturally and educationally mixed community. Health care professionals are well placed to encourage uptake of breast screening through disseminating information that promotes attendance, both within and outside the breast screening service. (Contains 8 tables.)