PTSD has been shown to be influenced genetically, and previous work has identified several possible genes that increase the risk of PTSD. Although several genomewide association studies (GWASs) have been conducted, the corresponding statistical power has been modest, and none included a Veteran-only population. The proposed study will address those deficiencies by conducting a well-powered case-control GWAS study in a large sample of US Veterans with PTSD as "cases" and psychiatrically-healthy Veterans as "controls."