The objective of this study is to estimate the causal effect of organized mammography screening programs on the proportion of women between 50 and 69 years of age who have ever used mammography. We exploit the gradual implementation of organized screening programs in nine Swiss cantons using a difference-in-difference approach. An analysis of four waves of the Swiss Health Survey shows that 3.5-5.4% points of the 87.9% utilization rate in cantons with screening programs in 2012 can be attributed to these organized programs. This effect indicates that organized programs can motivate women who have never done mammography to initiate screening.