Abstract: Background: Posttraumatic stress disorder (PTSD) is prevalent among military personnel. Cognitive processing therapy (CPT) is identified as one of the most effective treatments for PTSD, although smaller effects have been found in military populations. High rates of dropout from treatment may contribute to reduced efficacy, and military personnel may face unique barriers to treatment completion. One method of improving efficacy may be to reduce dropout by decreasing the time required to receive a full dose of treatment. This paper describes the design and methodology of the first randomized clinical trial testing whether CPT delivered in an intensive format is non-inferior to standard delivery of CPT. Method: Participants are 140 active duty service members randomized to receive CPT in a 5-day combined group and individual intensive outpatient format (MCPT) or standard CPT (delivered individually twice weekly over 6 weeks). Participants are assessed at baseline, and 1 month, 4 months, and 1 year following the conclusion of the therapy. Reduction in PTSD symptomatology is the primary outcome of interest. Secondary outcomes include comorbid psychological symptoms, health, and functioning. A secondary objective is to examine predictors of treatment outcome to determine which service members benefit most from which treatment modality. Conclusion: If determined to be non-inferior, MCPT would provide an efficient and accessible modality of evidence-based PTSD treatment. This therapy format would improve access to care by reducing the amount of time required for treatment and improving symptoms and functioning more rapidly, thereby minimizing interference with work-related activities and disruption to the mission.