Objective: To estimate the relative frequency and relative risk of post-traumatic stress disorder (PTSD) attributed to traumatic brain injury (TBI). Data Sources: PubMed and Embase were searched from database inception until January 26, 2019. Study Selection: Two independent investigators screened titles, abstracts, and full texts. We selected studies that included subjects presenting with TBI, and where the number of subjects with TBI and PTSD could be extrapolated. There were no restrictions on study design. Data Extraction and Synthesis: Data were extracted by two independent investigators and results were pooled using random-effects meta-analysis. Results: In civilian populations, relative frequency of PTSD following TBI was 12.2% after 3 months (CI-95 (7.6 to 16.8%) I² = 83.1%), 16.3% after 6 months (CI-95 (10.2 to 22.4%), I² = 88.4%), 18.6% after 12 months (CI-95 (10.2 to 26.9%), I² = 91.5%), and 11.0% after 24 months (CI-95 (0.0 to 25.8%), I² = 92.0%). Relative risk was 1.67 after 3 months (CI-95 (1.17 to 2.38), P = 0.011, I² = 49%), 1.36 after 6 months (CI-95 (0.81 to 2.30), P = 0.189, I² = 34%), and 1.70 after 12 months (CI-95 (1.16–2.50), P = 0.014, I² = 89%). In military populations, the relative frequency of associated PTSD was 48.2% (CI-95 (44.3 to 52.1%), I² = 100%) with a relative risk of 2.33 (CI-95 (2.00 to 2.72), P < 0.0001, I² = 99.9%). Conclusions and Relevance: TBI is a risk factor for PTSD in clinic-based civilian populations. There are insufficient data to assess the relative frequency or relative risk of PTSD in moderate to severe TBI. Due to significant between-study heterogeneity, the findings of our study should be interpreted with caution.