Aggressive behaviour is commonly observed among veterans with PTSD. Over a quarter of Iraq and Afghanistan veterans participated in physical aggression on return. This often involved severe violence, and of those seeking medical attention, over a half had PTSD. Such veterans with aggressive behaviours were strongly associated with hyperarousal and numbing symptom clusters, contributing to intimate partner violence. Alcohol misuse further amplifies risk: veterans with both PTSD and alcohol problems exhibit serious violence more than three times the rates of those with PTSD only. Combat exposure increases violent offending risk, with greater mission intensity predicting more offences. PTSD is associated with considerably elevated substance-related crimes, domestic violence and public disturbances. In conclusion, PTSD symptoms, especially that of chronic hyperarousal, and especially when combined with alcohol misuse and exposure to combat, substantially increase the likelihood of criminal behaviour in veterans.