Alcohol use in the military is a significant problem. The goal of this study was to examine the associations between personality, posttraumatic stress disorder (PTSD) symptoms, and postdeployment alcohol use disorders (AUDs) among a group of Operation Iraqi Freedom (OIF) deployed National Guard soldiers, with a focus on differentiating predeployment and postdeployment onset AUDs. Participants were 348 National Guard soldiers deployed to Iraq from March 2006 to July 2007 drawn from the Readiness and Resilience in National Guard Soldiers (RINGS) study. Participants completed self-report measures one month before deployment and 3 to 6 months postdeployment; current and lifetime history of AUDs were assessed 6 to 12 months postdeployment, using the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders (4th ed. text rev.; DSM–IV; American Psychiatric Association, 2000). Overall, 13% of the panel was diagnosed with a current AUD. Of those who met criteria for a current AUD, 38% had an AUD that developed following return from deployment (new onset AUD). The development of new onset AUDs was uniquely predicted by higher levels of PTSD symptom severity, higher levels of avoidance-specific PTSD symptoms, and lower levels of positive emotionality. AUDs with onset prior to deployment were predicted by higher levels of negative emotionality and disconstraint. Results of this study suggest that combat deployed soldiers with current AUDs are a heterogeneous group and point to the influence of combat-related PTSD symptoms in the development of AUDs following deployment.