This PTSD GWAS will compare 10,000 combat-exposed Veterans with PTSD to 10,000 combat-exposed controls. A to-be-selected microarray (see narrative) will be employed that contains approximately 245K genomewide association markers, 250K exonic markers and INDELs, 70K novel loss-of-function SNPs and INDELs, and 115K "custom" markers. Genotypes will be imputed to approximately 1KG for statistical analysis, and up to 50 putatively-associated SNPs that are initially imputed will be genotyped directly in the same sample.