We compared the impact of media vs. direct exposure on acute stress response to collective trauma. We conducted an Internetbased survey following the Boston Marathon bombings between April 29 and May 13, 2013, with representative samples of residents from Boston (n = 846), New York City (n = 941), and the remainder of the United States (n = 2,888). Acute stress symptom scores were comparable in Boston and New York [regression coefficient (b) = 0.43; SE = 1.42; 95% confidence interval (CI), −2.36, 3.23], but lower nationwide when compared with Boston (b = −2.21; SE = 1.07; 95% CI, −4.31, −0.12). Adjusting for prebombing mental health (collected prospectively), demographics, and prior collective stress exposure, six or more daily hours of bombing-related media exposure in the week after the bombings was associated with higher acute stress than direct exposure to the bombings (continuous acute stress symptom total: media exposure b = 15.61 vs. direct exposure b = 5.69). Controlling for prospectively collected prebombing televisionwatching habits did not change the findings. In adjusted models, direct exposure to the 9/11 terrorist attacks and the Sandy Hook School shootings were both significantly associated with bombing-related acute stress; Superstorm Sandy exposure wasn't. Prior exposure to similar and/or violent events may render some individuals vulnerable to the negative effects of collective traumas. Repeatedly engaging with trauma-related media content for several hours daily shortly after collective trauma may prolong acute stress experiences and promote substantial stress-related symptomatology. Mass media may become a conduit that spreads negative consequences of community trauma beyond directly affected communities.T he bombings at the 2013 Boston Marathon were the first major terror attacks on US soil since September 11, 2001 (9/11). As reporters' and spectators' cameras filmed the mayhem over the subsequent week, graphic images were shown repeatedly in both traditional and social media worldwide. Like the 9/11 attacks, the US population was the terrorists' intended psychological target.Widespread media coverage extends the boundaries of local disasters, transmitting their impact far beyond the directly exposed population and turning them into collective traumas with potentially detrimental health effects (1, 2). For example, television exposure to the Oklahoma City bombing (3), the 1990 Gulf War (4), and 9/11 (5-8) have all been associated with widespread diffusion of trauma-related symptoms soon after collective trauma. Early post-9/11 media exposure has even been prospectively associated with increases in 9/11-related posttraumatic stress (PTS) symptoms over 3 y following the attacks (9).Nonetheless, a prevailing assumption underlying professional response to collective trauma is that directly exposed individuals are, by definition, at greatest risk for stress-related disorders. This belief persists despite mounting evidence that both live and video observation of threatening content can lead to fea...