Minnesota recently became the 16th state to require facilities that perform mammograms to notify patients if they are found to have dense or extremely dense breasts, as this may make it more difficult to detect a cancer or put them at increased risk for cancer. This article outlines the new law and describes the classification system for breast density, the implications for breast density on screening mammography, and the relationship between breast density and cancer. It also provides guidance for patients who have dense breast tissue regarding supplementary screening.