Unexplained symptoms have frequently been observed in deployed Persian Gulf War veterans (GWVs). Using factor analysis, the Centers for Disease Control and Prevention (CDC) has established criteria for Gulf War illness (GWI). This article reports on the prevalence of GWI, identifies comorbidities, and compares these traits in 120 GWVs and veterans without GWI. Veterans with GWI were older; reported more combat exposure; scored higher on measures of depression, post-traumatic stress disorder, and fibromyalgia; and had poorer health-related quality of life. More than half had anxiety or depressive disorders, and 93% had at least one medical and/or psychiatric diagnosis. The Medical Outcomes Study Short Form predicted mental health status with a positive predictive value of 81.58. By adding the Hamilton D rating for depression, the positive predictive value increased to 88.57. The interpretation: The CDC criteria accurately identified GWVs negative for GWI. Most GWVs were positive for GWI. Neither CDC criteria nor CDC severity rankings distinguish between veterans with psychiatric syndromes and those without: both groups endorsed the same symptoms. More than half of those with GWI had a treatable anxiety or depressive disorder. Treatment suggestions are offered.