Overdiagnosis of breast cancer can result in overtreatment and cause physical and emotional harm. Based on data from 35,986 women in a US-based breast cancer screening registry, this study estimates that15.4% of screen-detected cancers are overdiagnosed (i.e., detecting indolent preclinical cancer or detecting progressive preclinical cancer among women who would have died of unrelated causes before clinical diagnosis), which is higher than previous estimates. The authors suggest that data can improve shared decision-making between patients and physicians.