Despite the important role of behavioral avoidance in the maintenance of post-traumatic stress disorder (PTSD), little is known about the role of implicit or reflexive avoidance tendencies in PTSD. The current dissertation examined the role of reflexive avoidance tendencies in individuals with PTSD in a series of three studies. First, we examined avoidance tendencies of trauma-related stimuli in military veterans with PTSD, trauma-exposed military veterans without PTSD, and non-trauma-exposed civilians. Compared to non-trauma exposed civilians, both veterans with and without PTSD showed greater reflexive avoidance of low arousal combat images, but only veterans without PTSD showed heightened reflexive avoidance of high arousal images. Additionally, re-experiencing symptom severity, but not other clusters of PTSD symptoms, was associated with reflexive avoidance of high arousal images and marginally associated with reflexive avoidance of low arousal images among veterans with and without PTSD. The second study focused on the relationship between automatic avoidance tendencies and neural activity in veterans with and without posttraumatic stress disorder. We found that veterans with and without PTSD exhibited heightened bilateral amygdala, right ventrolateral prefrontal cortex, and medial prefrontal cortex activation in response to combat (versus neutral) images, but this neural reactivity was not associated with avoidance tendencies. Finally, the third study examined the effect of inhibitory regulation training on fear responding, PTSD symptoms, and reflexive avoidance tendencies. Compared to a waitlist control condition, veterans who completed the training experienced significant reductions in self-reported PTSD symptoms and reduced reflexive avoidance of trauma-related images, but did not exhibit changes in physiological reactivity to trauma-related images from pre- to post-training. Our findings suggest that trauma-exposed veterans, regardless of whether they meet criteria for PTSD, exhibit reflexive avoidance of trauma-related stimuli, perhaps representing a behavioral indicator of trauma exposure. Additionally, though reflexive avoidance was not associated with neural activity within regions of the brain involved in emotional responding and inhibitory regulation, our findings do provide evidence that inhibitory regulation-based training may reduce reflexive avoidance behavior. Future research on this topic may elucidate our understanding of how to better address avoidance behaviors in PTSD treatment.