The effect of combat and operational stress on the mental health of military personnel is a major concern. The objective of this study was to identify factors associated with possible posttraumatic stress disorder (PTSD). A questionnaire was completed by 1,569 Marines who deployed in support of conflicts in Iraq and Afghanistan (2002–2007). Using the PTSD Checklist with a cutoff score of 44, 17.1% of the sample screened positive for possible PTSD. Of 9 demographic and psychosocial factors examined in relation to PTSD, 4 were significant in a multivariate analysis: deployment-related stressors, combat exposure, marital status, and education. Deployment-related stressors had a stronger association with PTSD than any other variable. This is an important finding because deployment-related stressors are potentially modifiable.