PTSD is associated with increased physical and psychological aggression in civilian, active duty, and veteran populations in the extant literature. That said, not all individuals with PTSD exhibit aggressive behaviors. As such, more work is needed to identify mediators and moderators of this relationship. The present study examined a conditional process model that examined 1) the degree to which depressive symptoms mediated the relationship between PTSD and both physical and psychological aggression, and, 2) whether any of the paths in the mediation model differed for individuals who screened positive for TBI versus those who did not. For the overall sample, the PTSD severity total effect was significant for both types of aggression, and depression was a significant mediator for psychological, but not physical, aggression. The multiple groups model showed that the indirect effect seen in the total sample existed only for those who had not screened positive for TBI, though the direct effect was significant for both groups. These findings help reconcile conflicting results from earlier studies and have important clinical implications, chiefly that individuals with PTSD should be monitored for psychological aggression regardless of TBI screening status, and that treating concurrent depressive symptoms may help reduce psychological aggression specifically for those who do not screen positive for TBI.