Background: Statistical literacy in health - the ability to properly understand medical evidence - is an important prerequisite to making informed medical decisions. Gigerenzer et al. (2008) define minimal statistical literacy in health as knowing, among other things, the following: First, physicians and patients should know that there is no certainty and no zero-risk, but only risk that is more or less acceptable; second, they should understand to what the risk refers exactly and whether it applies to them; third, they should understand that tests are not perfect and can make two errors, false alarms and misses; fourth, they should be aware that interventions have both benefits and harms; and fifth, they should be able to judge the quality of the evidence and detect conflicts of interest. Objectives: To assess the degree of statistical literacy in health with regard to mammography screening in a highly motivated group of women who visited a mammography screening facility on an open day information session for women ages 50 to 69 in Germany. Methods: More than 90% of visitors participated in the study; half of them were surveyed before and after their visit, and the other half only after their visit. The final sample for the analyses consisted of 58 women of age 40 or older. We assessed how well they were informed about risks and benefits, which is important in face of a nationwide program for screening that has just started in Germany. Results: The group of highly motivated women largely overestimated both the benefits of screening and the predictive power of positive test results. Moreover, knowledge about the benefits did not improve after the visit. Even more worrying, the number of women who correctly believed that screening has also harms decreased from 60% before to 40% after the visit. A most important result of this survey was that the women did not question whether screening has any benefits or not. Instead, the benefit of screening was more or less blindly assumed. Conclusions: Women who make a particular effort to inform themselves do not really make an informed decision whether to undergo screening or not.