We conducted a retrospective study of 473,964 U.S. Army soldiers deployed to Iraq and Afghanistan through December 2004 using deployment and admission records. We categorized mental disorder diagnoses using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) and identified attempted suicide/ self-inflicted injuries using ICD-9-CM diagnosis codes E950-E959. We estimated and evaluated relative risks (RR) using Poisson regression models. Analysis found 1,948 psychiatric hospitalizations of deployed soldiers. The most common mental problems were mood, adjustment, and anxiety disorders (including post-traumatic stress disorder [PTSD]). RR of mental disorders ranged from 1.6 to 3 for females and 2 to 6 for enlisted soldiers compared to their counterparts. Younger soldiers had 30-60% higher substance abuse disorders. Combat units in Iraq demonstrated higher risk of any mental disorder and anxiety problems compared to combat support units. Younger women had the highest incidence of attempted suicide/ self-inflicted injuries. Further mental disorders surveillance is recommended.