This prospective study examined: (a) the effects of Iraq War deployment versus non-deployment on pre- to postdeployment change in PTSD symptoms and (b) among deployed soldiers, associations of deployment/postdeployment stress exposures and baseline PTSD symptoms with PTSD symptom change. Seven hundred seventy-four U.S. Army soldiers completed self-report measures of stress exposure and PTSD symptom severity before and after Iraq deployment and were compared with 309 soldiers who did not deploy. Deployed soldiers, compared with non-deployed soldiers, reported increased PTSD symptom severity from Time 1 to Time 2. After controlling for baseline symptoms, deployment-related stressors contributed to longitudinal increases in PTSD symptoms. Combat severity was more strongly associated with symptom increases among active duty soldiers with higher baseline PTSD symptoms.