The main aim of national breast screening is a reduction in breast cancer mortality. The data on the reduction in breast cancer mortality from three (of the five) Swedish trials in particular gave rise to the expectation that the Dutch programme of 2-yearly screening for women aged 50-70 would produce a 16% reduction in the total population. In all likelihood, many of the years of life gained as a result of screening are enjoyed in good health. According to its critics the actual benefit that can be achieved from the national breast cancer screening programmes is overstated. Considerable benefits have recently been demonstrated in England and Wales. However, the fall was so considerable in such a relatively short space of time that screening (started in 1987) was thought to only have played a small part. As far as the Dutch screening programme is concerned it is still too early to reach any conclusions about a possible reduction in mortality. The first short-term results of the screening are favourable and as good as (or better than) expectations. In Swedish regions where mammographic screening was introduced, a 19% reduction in breast cancer mortality can be estimated at population level, and recently a 20% reduction was presented in the UK. In countries where women are expected to make appointments for screening themselves, the attendance figures are significantly lower and the quality of the process as a whole is sometimes poorer. The benefits of breast cancer screening need to be carefully balanced against the burden to women and to the health care system. Mass breast screening requires many resources and will be a costly service. Cost-effectiveness of a breast cancer screening programme can be estimated using a computer model. Published cost-effectiveness ratios may differ tremendously, but are often the result of different types of calculation, time periods considered, including or excluding downstream cost. The approach of simulation and estimation is here the same for all countries. The effects of a breast-screening program depend on many factors, such as the epidemiology of the disease, the health care system, costs of health care, the quality of the screening programme and the attendance rate. The estimated CE-ratio ranges from 2650 euros per life-year gained in Navarra to 9650 in Germany. Although relatively low incidence levels expected, the CE-ratio in Navarra is most favourable probably due to a relatively unfavourable clinical stage distribution before screening and the increasing incidence. The UK has a screening situation that is almost similar with the Netherlands. Therefore, the CE-ratios of both countries are comparable. The differences between countries make it impossible to set up one uniform screening policy. The theoretical outcomes of the benefit that can be achieved are generally from small-scale trials involving a limited number of experts, persons examined, and areas. On a national scale, with hundreds of professional practitioners, it can be expected to be more difficult to attain uniform quality. Continuous quality control, monitoring and evaluation are therefore crucial.