The present investigation examined associations between intensities of exercise involvement and posttraumatic stress (PTS) symptom cluster severity (reexperiencing, avoidance/numbing, and hyperarousal). The sample was comprised of 108 adults (54.6% women; M_age = 23.9, SD = 10.22, range = 18–62), who endorsed exposure to a Diagnostic and Statistical Manual of Mental Disorders (Fourth edition, Text Revision) posttraumatic stress disorder Criterion A traumatic life event but did not meet criteria for any current Axis I psychopathology. After controlling for gender and lifetime number of trauma exposure types experienced, results indicated that vigorous-intensity exercise, but not light- or moderate-intensity exercise, was significantly inversely associated with hyperarousal symptom cluster severity. This study adds to the scarce, yet growing, body of exercise—PTS literature—by illuminating the inverse associations of vigorous-intensity exercise, specifically, and PTS hyperarousal symptom severity among trauma-exposed individuals.