This study examines gender differences in post-traumatic stress symptoms (PTSS) and PTSS risk/protective factors among soldiers deployed to Iraq. We pay special attention to two potentially modifiable military factors, military preparedness and unit cohesion, which may buffer the deleterious psychological effects of combat. Longitudinal data were collected on 922 New Jersey National Guard soldiers (91 women) deployed to Iraq in 2008. Anonymous surveys administered at pre- and post-deployment included the PTSD Checklist (PCL), the Unit Support Scale, and a preparedness scale adapted from the Iowa Gulf War Study. Bivariate analyses and hierarchical multiple regression were used to identify predictors of PTSS and their explanatory effects on the relationship between gender and PTSS. Women had a higher prevalence of probable post-deployment PTSD than men (18.7% vs. 8.7%; OR = 2.45; CI [1.37, 4.37]) and significantly higher post-deployment PTSS (33.73 vs. 27.37; p = .001). While there were no gender differences in combat exposure, women scored higher on pre-deployment PTSS (26.9 vs. 23.1; p ≤ .001) and lower on military preparedness (1.65 vs. 2.41; p ≤ .001) and unit cohesion (32.5 vs. 38.1; p ≤ .001). In a multivariate model, controlling for all PTSS risk/resilience factors reduced the gender difference as measured by the unstandardized Beta (B) by 45%, with 18% uniquely attributable to low cohesion and low preparedness. In the fully controlled model, gender remained a significant predictor of PTSS but the effect size was small (d = .26). Modifiable military institutional factors may account for much of the increased vulnerability of women soldiers to PTSD.