Volume 36/Number 4/October 2014/Pages 360-376 Effectiveness of Cognitive Processing Therapy for Treating Posttraumatic Stress Disorder Stephen Lenz Brian Bruijn Nina S. Serman Laura Bailey Analyzing 11 studies, we evaluated the effectiveness of cognitive processing therapy (CPT) for treating posttraumatic stress disorder (PTSD) and co-occurring depression symptoms in individ- uals diagnosed with PTSD. Separate meta-analytic procedures for between-group studies using waitlist or alternative treatment comparisons yielded large to very large effect sizes for CPT ver- sus waitlist, and medium to large effect sizes when CPT was compared to alternative treatments. Implications for evidence-supported practice and study limitations are discussed. Posttraumatic stress disorder (PTSD) is a clinical syndrome characterized by intrusive memories, emotional avoidance, and heightened physiologi- cal arousal following exposure to a traumatic event (American Psychiatric Association [APA], 2000, 2013). The National Institute for Mental Health (2005) estimated that about 21 million individuals within the United States experience symptoms associated with PTSD; however, there is a burgeoning perception that prolonged military engagements may presage an increase in prevalence over the next decade (Hoge, Auchterlone, & Milliken, 2006; Schell & Marshall, 2008). Over the lifespan women report PTSD symptoms to a greater degree than men (Ditlevson & Elklit, 2010; Kessler et ah, 2005) and the degree to which an individual is exposed to deleterious influences, such as highly perilous vocations, partner violence, poverty, and lack of social support may heighten the risk for PTSD (Brewin, Andrews, & Valentine, 2000; Taylor & Baker, 2007). The prevalence of this syndrome across population subgroups is worrisome given that mood disorders like PTSD are among those most fre- quently associated with disability (Social Security Administration, 2011) and lethality (Nepon, Belik, Bolton, & Sareen, 2010; Sabri et ah, 2013). When comparing individuals with PTSD to those without, researchers have identified a number of pervasive and detrimental trends, such as restricted peer relations (Laffaye, Cavella, Drescher, & Rosen, 2008); low academic Stephen Lenz is affiliated with Texas A&M University-Corpus Christi, and Brian Bruijn, Nina S. Serman, and Laura Bailey with The University of Memphis. Correspondence about this article should be directed to A. Stephen Lenz, Texas A&M University-Corpus Christi, Department of Counseling and Educational Psychology, ECDC 152, Corpus Christi, Texas, 78412. Email: Stephen.Lenz@tamucc.edu. 360 0 Journal of Mental Health Counseling