This study examined the mental health and functional consequences associated with killing combatants and noncombatants. Using the National Vietnam Veterans Readjustment Study (NVVRS) survey data, the authors reported the percentage of male Vietnam theater veterans (N = 1200) who killed an enemy combatant, civilian, and/or prisoner of war. They next examined the relationship between killing in war and a number of mental health and functional outcomes using the clinical interview subsample of the NVVRS (n = 259). Controlling for demographic variables and exposure to general combat experiences, the authors found that killing was associated with posttraumatic stress disorder symptoms, dissociation, functional impairment, and violent behaviors. Experiences of killing in war are important to address in the evaluation and treatment of veterans. © 2009 International Society for Traumatic Stress Studies.