Background: Mindfulness for posttraumatic stress disorder (PTSD) is discussed controversially. Therefore, we meta-analyzed the effectiveness and safety of mindfulness-based interventions in PTSD patients. Methods: We searched CENTRAL, PubMed, PsychInfo, and Scopus until April 2018. Eligible criteria included randomized controlled trials (RCT) on Mindfulness-Based Stress Reduction (MBSR) and Mindfulness-Based Cognitive Therapy (MBCT) against treatment as usual (TAU) or other active interventions. Standardized mean differences (SMD), 95% confidence intervals (CI), and heterogeneity (I2) were calculated for primary (PTSD severity) and secondary (depression and quality of life) outcomes post intervention (PI) and follow-up 6 months after randomization (6MFU). Risk of bias was assessed by the Cochrane risk of bias tool. Results: The search revealed eight RCTs on MBSR and two on MBCT including 484 veterans with DSM-IV/V PTSD. Except for two RCTs, risk of bias was mostly unclear to high. Compared to TAU, MBSR showed significant and consistent greater effects for PI quality of life (2 RCTs, SMD = 0.97, 95%CI = [0.28 | 1.66], I2 = 47%, p = 0.17, N = 75), PI depression (4 RCTs, SMD = −0.65, 95%CI = [−0.96 | −0.33], I2 = 20%, p = 0.29, N = 208), and 6MFU depression (2 RCTs, SMD-0.68, 95%CI = [−1.12 | −0.23], I2 = 0%, p = 0.58, N = 82). Compared to psychoeducation or sham-therapy, MBSR/MBCT revealed significant but inconsistent greater effects for PI PTSD severity (2 RCTs, SMD-1.76, 95%CI = [−2.76 | −0.77], I2 = 69%, p = 0.07, N = 75). Compared to Present Centered Group Therapy, MBSR/MBCT did not reveal significant greater effects. Serious adverse events were reported by three RCTs as being equally contributed between groups. Conclusion: Based on high-quality RCTs, MBSR or MBCT cannot be recommended for PTSD to date. Further research particularly in civilians is warranted.