Gulf War Illness (GWI) is a multi-symptom disease of unknown etiology that was observed in veterans after the first Gulf War (1990-1991). GWI involves multiple organ systems and has symptoms suggesting the involvement of the immune system. Many studies show Human Leukocyte Antigen (HLA) associations with autoimmune, infectious, and inflammatory diseases. Researchers have hypothesized that the multi-symptom nature of GWI may share an autoimmune component. In order to test for a potential immunological component in GWI, we test the hypothesis that HLA might differ between veterans with GWI compared to Gulf War era veterans without GWI.