Although researchers have questioned their coverage and accuracy, the media routinely are used as sources of data on mass murder in the United States. Databases compiled from media sources such as newspaper and network news programs include the New York Police Department’s Active Shooters file, the Brady Campaign Mass Casualty Shootings data set, and the Mother Jones database. Conversely, official crime data have been underutilized by researchers who study mass murder (for exceptions, see Duwe, 2007; Fox & Levin, 1998). In this study, we compare similarities and differences for mass murder cases in the United States as portrayed by selected mass media sources. Then, we turn our focus to a comparison of the Uniform Crime Reports’ (UCR) Supplementary Homicide Report (SHR) and the National Incident-Based Reporting System (NIBRS). Our primary focus is on mass murders involving four or more fatalities—not including the perpetrator—that have occurred between 2001 and 2010. Implications for enhancing the comprehensiveness and quality of mass murder data with the goal of increasing their usefulness for guiding prevention and risk mitigation efforts also are discussed.