Objectives: To assess outcomes of veterans who participated in mindfulness-based stress reduction (MBSR). Design: Posttraumatic stress disorder (PTSD) symptoms, depression, functional status, behavioral activation, experiential avoidance, and mindfulness were assessed at baseline, and 2 and 6 months after enrollment. Results: At 6 months, there were significant improvements in PTSD symptoms (standardized effect size, d = -0.64, p< 0.001); depression (d = -0.70, p<0.001); behavioral activation (d = 0.62, p<0.001); mental component summary score of the Short Form-8 (d = 0.72, p<0.001); acceptance (d = 0.67, p<0.001); and mindfulness (d = 0.78, p<0.001), and 47.7% of veterans had clinically significant improvements in PTSD symptoms. Conclusions: MBSR shows promise as an intervention for PTSD and warrants further study in randomized controlled trials. © 2011 Wiley Periodicals, Inc. J Clin Psychol 68:1–16, 2012.