Participants were recruited from female undergraduate students participating in an ongoing longitudinal study at the time of a campus shooting. Eighty-five percent (N = 691) of the 812 students who were invited to participate in the current study completed questionnaires an average of 27 days following a campus shooting. In a mixed cross-sectional and longitudinal design, the cognitive and the physical concerns dimensions of postshooting anxiety sensitivity accounted for unique variance in posttrauma stress symptom severity (cross-sectional), after controlling for preshooting psychological symptoms (longitudinal). The cognitive concerns dimension showed the strongest relationship. Anxiety sensitivity also appeared to moderate the relationships of hyperarousal symptoms with reexperiencing and numbing symptoms.