This study examined the mental health impact of reported direct and indirect killing among 2,797 U.S. soldiers returning from Operation Iraqi Freedom. Data were collected as part of a postdeployment screening program at a large Army medical facility. Overall, 40% of soldiers reported killing or being responsible for killing during their deployment. Even after controlling for combat exposure, killing was a significant predictor of posttraumatic disorder (PTSD) symptoms, alcohol abuse, anger, and relationship problems. Military personnel returning from modern deployments are at risk of adverse mental health conditions and related psychosocial functioning related to killing in war.Mental health assessment and treatment should address reactions to killing to optimize readjustment following deployment. © 2010 International Society for Traumatic Stress Studies.