Decades of evidence reveal a complicated relationship between mammograms and mortality. Mammograms may detect deadly cancers early, but they may also lead to the diagnosis and potentially fatal treatment of cancers that would never progress to cause symptoms. I provide a brief history of the evidence on mammograms and mortality, focusing on evidence from clinical trials, and I discuss how this evidence informs mammography guidelines. I then explore the evolution of all-cause mortality relative to breast cancer mortality within an influential clinical trial. I conclude with some responses to the evolving evidence.