Rationale. Posttraumatic stress disorder (PTSD) is characterized by a constellation of symptoms including intrusive thoughts, avoidance, negative thoughts and mood, and alterations in reactivity following exposure to a traumatic event. Despite the availability of effective treatments for PTSD in the Veterans Administration (VA) Healthcare System, PTSD treatment utilization and completion is low. The goal of this study was to better understand how personlevel demographic, psychosocial, and psychiatric variables as well as treatment setting systems variables are related to evidence-based treatment utilization, completion, and symptom improvement among OEF/OIF/OND veterans with PTSD. Design. OEF/OIF/OND veterans with PTSD (N = 311) were recruited at a pre-treatment orientation group at a VA outpatient PTSD clinic and classified into one of six groups based on their utilization of evidence-based psychotherapy within a 12-month period: (1) decliners of all treatment options, (2) medication only, (3) non-EBP psychotherapy utilizers, (4) EBP dropouts, (5) EBP treatment completers, and (6) EBP high utilizers. Next, Andersen's Behavioral Model of Health Care Utilization was used as a framework to better understand factors associated with utilization, completion, and symptom improvement through three specific aims. Aim 1: Using analyses of variance, explore differences in baseline predisposing characteristics, enabling resources, and need factors among utilization groups. Aim 2: Using logistic regression, explore the predictive utility of predisposing characteristics, enabling resources, and need factors as they related to evidence-based psychotherapy treatment completion. Aim 3: Using repeated measures ANOVAs, explore how predisposing characteristics, enabling resources, and need variables related to PTSD and depression symptom change following evidence-based psychotherapy treatment completion. Results. Aim 1: Reporting use of the GI Bill was much less likely among EBP high utilizers than veterans in the other groups. Distance to the hospital was associated with utilization, such that decliners of all treatment and non-EBP psychotherapy users traveled an average of 27-29 miles to the VA, while veterans in the other utilization groups traveled an average of 19-22 miles. Previously receiving psychiatric care prior to attending the PTSD clinic was associated with increased utilization. Aim 2: Receiving EBP through a research study or a comorbid substance use disorder were significantly associated with being an EBP dropout. Reporting a problem with family members or significant others at intake was associated with being an EBP treatment completer. Aim 3: Participating in EBP in a group format, a comorbid diagnosis of depression, or reporting problems with anger or sleep were all associated with less change in PTSD symptoms following EBP. Reporting use of the GI Bill or problems with anger were associated with larger decreases in PTSD symptoms after treatment. Conclusions. Using Andersen's Behavioral Model, we found that certain enabling resources and need factors were related to aspects of utilization, completion and symptom change while predisposing characteristics were not. These results are relevant to improving veteran treatment outcomes because enabling resources (e.g., treatment format) and need factors (e.g., comorbid depression) are potentially modifiable targets for intervention while predisposing factors (e.g., age, gender) are not. Future work seeking to better understand if a causal relationship between these variables and treatment engagement is the next step to better inform if modification will lead to improved EBP utilization and completion.