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The long term effect of mammographic service screening is not well established. We aimed to assess the long-term effect of mammographic screening on death from breast cancer, taking into account potential biases from self-selection, changes in breast cancer incidence, and classification of cause of death.

We compared deaths from breast cancer diagnosed in the 20 years before screening was introduced (1958–77) with those from breast cancer diagnosed in the 20 years after the introduction of screening (1978–97) in two Swedish counties, in 210 000 women aged 20–69 years. We also compared deaths from all cancers and from all causes in patients diagnosed with breast cancer in the 20 years before and after screening was introduced. In the analysis, data were stratified into age-groups invited for screening (40–69 years) and not invited (20–39 years), and by whether or not the women …