Posttraumatic Stress Disorder (PTSD) is debilitating and common (up to 30% in Vietnam Veterans and 16% in Afghanistan and Iraq Veterans). A significant number of Veterans do not engage in or drop-out from effective trauma-focused therapies due to avoidance from trauma-related memories. Because of this limitation, and because scientific literature suggested that acupuncture might be effective for PTSD symptoms, the investigators developed an acupuncture intervention for PTSD and conducted a clinical trial that showed positive effects. This remains the only high quality trial of acupuncture for PTSD published, because of which the current VA/DoD guidelines for PTSD state that acupuncture is a "B" recommendation (fair evidence, provide service) for PTSD treatment. That civilian study compared acupuncture to an effective therapy (CBT) and a wait-list control, but did not have a placebo control. And, research has shown that Veterans may respond differently to therapies than civilians. More definitive data about the efficacy of acupuncture for PTSD is required in order to recommend it as an "A" evidence-based intervention for PTSD in Veterans. Specifically, it is important to show that acupuncture is better than a placebo control and that it has effects on biological abnormalities of PTSD. The aim of this study is to demonstrate efficacy of acupuncture for PTSD by showing clinical and biological effects that are statistically larger and clinically more important than effects of "sham" acupuncture. Given current knowledge and the need for efficient, ethical and best practices within an experimental design, the primary aim is best accomplished by a randomized controlled trial comparing verum acupuncture (ACU) to placebo minimal needling sham acupuncture (MIN). The goal is to evaluate ACU for a significant positive signal, not to compare ACU to other interventions or to evaluate treatment durability. Acupuncture is delivered in 24 sessions over 12 weeks. The primary hypothesis is that efficacy of ACU for PTSD symptom severity will be large (pre- to post-treatment Cohen's d \> 0.8), and significantly better than MIN (between group Cohen's d \> 0.30, with 80% probability of detecting a true group difference at p\<0.05 (2-sided). The secondary hypothesis is that compared to MIN, ACU will be associated with a significantly larger change from pre- to post-treatment in psychophysiological response (decreased startle by EMG eyeblink during fear conditioning procedure). The study design is a two-arm, parallel-group, prospective randomized controlled trial (RCT). The sample frame is Veterans with chronic PTSD with a sample of convenience from those seeking care at the Long Beach VA. Exclusion criteria are meant to keep out individuals with characteristics that are known to be PTSD treatment confounds, associated with non-adherence or negative response to treatment, that may significantly affect biological assessment, or who may be put at risk of harm. The sample size (90) provides adequate power to test hypotheses. Subjects will be allocated to intervention group by computer-generated adaptive randomization. General linear mixed models will be used to evaluate hypothesized effects over time (mid treatment, end of treatment, 1-month follow-up), controlling for baseline severity of symptoms and demographic characteristics (e.g., age, gender) using intent-to-treat modeling. Outcome effect size (Cohen's d) within and between subjects will be calculated. Interaction terms will be included in the models to evaluate treatment fidelity and treatment expectancy as potential moderators. Study results will provide clinicians and policy makers with more information to make decisions about the rational use of acupuncture for PTSD. This is important because acupuncture is being touted for PTSD by many advocates. It has the potential to reach PTSD sufferers who are not willing to engage in trauma-focused psychotherapy, or for whom current therapies are ineffective. The objective of this project is consistent with priority research areas of specific interest to Clinical Science Research \& Development (CSR\&D) including PTSD and complementary medicine, and all participants are Veterans at a VA Hospital.