QUESTIONS UNDER STUDY:In Switzerland controversy exists on how to summarise the evidence on the efficacy and effectiveness, as well as adverse effects, of mammography screening, and breast cancer mortality trends are often discussed in the context of the impact of mammography. PRINCIPLES/METHODS: Single-study publications, meta-analyses, and reports by international expert groups on mammography screening are reviewed. Breast cancer mortality trends from 1970-2000 are reported and discussed in the context of the Swiss screening situation. RESULTS:In Switzerland breast cancer mortality rates for female Swiss nationals aged 50-79 years fell between 1990 and 2000 by some 25% in all language regions. The data from randomised studies in large populations in several countries with well organised mammography programmes prompt the conclusion that participation in organised screening programmes with rigorous quality standards reduces breast cancer mortality. The achievable long-term reduction in breast cancer mortality ranges from 5-20% in the target population provided that appropriate diagnostic investigation and treatment are available. To achieve this in Switzerland 830 to 3300 women need to be invited to screening for ten years to prevent one death from breast cancer. The risk-benefit profile of mammography screening is likely to be less favourable if mammographies are performed outside the context of organised screening programmes. In Switzerland we are now confronted with growing regional disparities in access to screening mammography which is under systematic quality control. CONCLUSIONS:The decrease in breast cancer mortality in Switzerland is most probably due to treatment developments and changes in cause-of-death coding. Public health measures in Switzerland should aim at regulating quality control for screening mammography, monitoring mammography use and improving the information on mammography available to women. For an evidence-based decision regarding health insurance coverage of screening mammography in 2007, large gaps need to be filled. The current coexistence of systematic screening programmes and opportunistic screening, with distinct regional differences, provides a unique opportunity for research into the merits and drawbacks of the two approaches.