This study examined the association between posttraumatic stress disorder (PTSD) symptomatology and aggressive behavior among a sample of male Vietnam veterans (N = 1,328). Results indicated that the hyperarousal PTSD symptom cluster evidenced the strongest positive association with aggression at the bivariate level when compared with the other PTSD symptom clusters. When the PTSD symptom clusters were examined together as predictors, hyperarousal symptoms evidenced a significant positive relationship with aggression, and avoidance/numbing symptoms were negatively associated with aggression. Examination of potential mediators indicated that hyperarousal symptoms were directly associated with aggression and indirectly related to aggression via alcohol problems. Reexperiencing symptoms were associated with aggression only indirectly and through their positive association with physiological reactivity and negative association with alcohol problems. Study results highlight the complexity of the relationship between PTSD symptoms and aggression, and suggest possible mechanisms explaining this association.