Structural equation modeling was used to examine relationships among prewar factors, dimensions of war-zone stress, and current posttraumatic stress disorder (PTSD) symptomatology using data from 1,632 female and male participants in the National Vietnam Veterans Readjustment Study. For men, previous trauma history (accidents, assaults, and natural disasters) directly predicted PTSD and also interacted with war-zone stressor level to exacerbate PTSD symptoms for high combat-exposed veterans. Male veterans who entered the war at a younger age displayed more symptoms. Family instability, childhood antisocial behavior, and age had indirect effects on PTSD for men. For women, indirect prewar effects emanated from family instability. More attention should be given to critical developmental conditions, especially family instability and earlier trauma exposure, in conceptualizing PTSD in adults.