Posttraumatic stress disorder (PTSD) symptoms and poor sleep have been identified as potential causals factor in aggression, violence, and impulsive behavior. Given the high cost of aggression to society and public health, identifying modifiable factors related to aggression, such as insomnia, may guide treatment strategies to help decrease aggression. Participants were 143 Veterans seeking treatment for PTSD at a VA outpatient PTSD clinic. Linear and logistic regression analyses were used to examine the relation between PTSD and insomnia on aggression. Results from bivariate analyses indicated that while both PTSD and insomnia severity were associated with higher aggression scores independently, when PTSD and insomnia were examined together, PTSD severity was the only significant predictor of aggression. Interaction effects yielded nonsignificant results suggesting that poor sleep did not moderate the PTSD and aggression relation. Results suggest that addressing PTSD symptoms as a first treatment target may be more important for decreasing risk for aggression than targeting insomnia. More research is needed to understand whether treating PTSD and insomnia reduces aggression in Veterans.