The purpose of this study is to improve the efficiency of treatment for post-traumatic stress disorder (PTSD) with prolonged exposure (PE), an efficacious treatment for PTSD typically administered in once- or twice-weekly sessions. We will evaluate whether massing 10 PE sessions in 2 weeks (massed trials; M-PE) is more efficacious than Minimal Contact control (MCC); 2) whether the massed sessions format retains the efficacy of treatment compared to 10 PE sessions spaced over 8 weeks (spaced trials; S-PE), and 3) will evaluate for the first time the efficacy of the 10 PE sessions delivered in 8 weeks in an active duty population by comparing it to an active comparison condition, Present-Centered Therapy (PCT). Randomization was initially set at 3:11:11:11 for MCC:M-PE:S-PE:PCT. Due to the urgent need for data to inform military clinical practice, enrollment in MCC was accelerated by changing the ratio to 1:1:1:1 in order to report the comparison between M-PE and MCC. When 30 participants were enrolled in MCC, randomization resumed to approximately 3:11:11:11. Prolonged Exposure (PE; Foa, Hembree, & Rothbaum, 2007; Foa & Rothbaum, 1998) was developed by the PI, Edna Foa, and colleagues in the Center for the Treatment & Study of Anxiety (CTSA), University of Pennsylvania. It has been found quite efficacious in reducing PTSD and related psychopathology with various types of trauma in PTSD centers around the world. Furthermore, PE has been identified in the joint VA-Department of Defense Clinical Practice Guideline for PTSD (VA-DoD Clinical Practice Guideline Working Group, 2003) as "strongly recommended" for use with veterans with PTSD, based on the strong empirical support for PE.