In the "Diagnostic and Statistical Manual of Mental Disorders" (4th ed., text rev., "DSM-IV-TR"; American Psychiatric Association, 2000), posttraumatic stress disorder (PTSD) Criterion A2 stipulates that an individual must experience intense fear, helplessness, or horror during an event that threatened the life or physical integrity of oneself or others to be eligible for the PTSD diagnosis. In considering this criterion, we describe its origins, review studies that have examined its predictive validity, and reflect on the intended purpose of the criterion and how it complements the mission of the "DSM". We then assert that the predictive validity of Criterion A2 may not be an appropriate metric for evaluating its worth. We also note that the current Criterion A2 may not fully capture all the salient aspects of the traumatic stress response. To support this claim, we review empirical research showing that individuals adapt to extreme environmental events by responding in a complex and coordinated manner. This complex response set involves an individual's appraisal regarding the degree to which the event taxes his or her resources, as well as a range of other cognitions (e.g., dissociation), felt emotions (e.g., fear), physiological reactions (e.g., heart rate increase), and behaviors (e.g., tonic immobility). We provide evidence that these response components may be associated with the subsequent development of PTSD. We then describe the challenges associated with accurately assessing an individual's traumatic stress response. We conclude with a discussion of the need to consider the individual's immediate response when defining a traumatic stressor. (Contains 1 figure.)