This study conducted a meta-analysis of published randomized clinical group trials for adult survivors of trauma to examine the efficacy of the group format. Effect sizes for posttraumatic stress disorder (PTSD) severity outcome were examined. Sixteen studies were included, with a total of 1686 participants. Results of a random effects model meta-analysis indicated that group treatments are associated with significant pre- to posttreatment reduction in PTSD symptom severity (within treatment d = .71, 95% CI [.51, .91]), and result in superior treatment effects relative to a wait list comparison condition (d = .56, 95% CI [.31, .82]). However, no significant findings were obtained for group interventions relative to active treatment comparison conditions (d = .09, 95% CI [−.03, .22]). Moderator analyses also indicated that gender and type of trauma moderated treatment effects for PTSD outcome, with smaller effect sizes associated with males relative to females and combined gender samples, and smaller effect sizes for combat and child sexual assault trauma samples relative to mixed-trauma sample studies. Taken together, group treatment for trauma symptoms is better than no treatment but not better relative to comparison conditions that control for nonspecific benefits of therapy. Additional work is needed to identify effective group treatments for PTSD, especially for patients with repeated or chronic traumatization.