© 2019 Guilford Publications. All rights reserved. Objective: Prior work suggests that people function effectively in the world, in part, by relying on sociocultural anxiety-buffer systems to protect against death anxiety. However, traumatic experiences may overwhelm and disrupt those systems, and this work tests whether posttraumatic stress symptoms reflect a vulnerability to death anxiety and risk of coping failure. Method: Following posttraumatic stress screening (n = 4129), individuals with low (n = 187) and high (n = 186) posttraumatic stress symptoms engaged in either an anxiety-buffer stressor task (contemplating relationship problems) or control task. Participants subsequently reported death anxiety and made coping appraisals. Results: Results supported four key hypotheses. Among individuals with low posttraumatic stress: (1) death anxiety was low under control conditions but moderately increased after contemplating relationship problems; and (2) perceived coping ability remained high in both conditions. However, among those with high posttraumatic stress: (3) death anxiety was exceptionally high in both the relationship problems prime and the control conditions-indicating anxiety buffer disruption; and (4) perceived coping ability was low in the control condition, and even lower after contemplating relationship problems. Conclusions: These findings support the hypotheses and make novel contributions, in that prior research on the existential implications of PTSD have not considered that anxiety buffer disruption may be associated with failure to cope with new challenges after traumatic experiences. Future research should determine whether therapies can improve the core dimensions of functional worldviews, a sense of meaning and self-esteem, and whether such improvements result in improvements to perceived coping abilities.