Objective: Few studies have examined the impact of military sexual trauma (MST) on social functioning during deployment. Yet consideration of unit relationships during deployment may be important, given that military unit cohesion and support can provide protective effects against the stress of combat, and reduce the likelihood of developing posttraumatic stress disorder. Method: Although prior research has posited that depleted social resources are one pathway through which MST is associated with posttraumatic stress symptoms (PTSS), no studies have statistically tested this theory. This study examined the association of MST and PTSS and evaluated the potential mediating role of decreased unit relationship quality. Mediational analyses were conducted on a sample of veterans following discharge from military service (N = 818; 328 women, 490 men). Results: Women were significantly more likely to experience MST than men. As hypothesized, experiences of MST during deployment were associated with higher PTSS. MST experiences were associated with less trust in and support from one’s military unit, which partially mediated the association between MST and PTSS. The indirect effect of MST on PTSS through lower unit relationship quality accounted for 20.4% of the total effect of MST on PTSS. Conclusions: While the retrospective study design precludes tests of causality, mediational findings provided statistical evidence that lower unit relationship quality partially explains the association between MST and PTSS. This finding is consistent with interpersonal theories of trauma response suggesting that the deleterious effects of MST may be in part due to its erosion of social resources during deployment.