Breast cancer screening using mammography is one of the few screening interventions that have been assessed in several large randomized controlled studies (RCTs). Results from eight RCTs are available and have been summarized in several systematic reviews and meta-analyses, most of which conclude that mammography screening achieve a relative reduction in breast cancer mortality of 20 %. In the Swiss context this translates to one prevented breast cancer death over 10 years among 1000 women who start biannual mammography screening at age 50. However, mammography screening leads to the detection of cancers that would never have been found were it not for the screening (overdiagnosis). Screening thus increases the incidence of breast cancer, by about 20 %, which in turn leads to more therapies (surgery, radiation and chemotherapy). Over ten years after starting mammography at age 50, four additional women out of 1000 will be diagnosed with breast cancer. Without screening, these women would not have had a diagnosis. Over the same ten years (five screening rounds), about one in five women will have at least one mammography result which requires further diagnostic workup. Furthermore, even when mammography screening is implemented, 20 to 30 % breast cancer patients will not be diagnosed by the screening but between screening rounds. The information and knowledge of the population about benefits and harms of mammography screening is inadequate in that the benefits are overestimated and the harms underestimated. The female population needs to be better informed on both these aspects of mammography screening. Women have a right to receive adequate evidence-based information in order to make an informed decision whether to attend mammography screening.