Research has documented higher risks for mental health problems among service members deployed to war zones, yet a research limitation has been that assessment has generally occurred often years after combat exposure. The Operational Stress Control and Readiness program integrated mental health practitioners with 1st Marine Division units serving in Iraq. This team documented mental health visits between January 2006 and January 2007 and developed the Theater Mental Health Encounter Database (TMHED). This report describes the TMHED study design, measures, and cases. Of 1336 patients (3180 patient visits), 10% were women, 75% were high school educated, 55% were mid-paygrade enlisted, and 63% were on their first combat deployment. Compared with the overall deployed population, patient percentages included higher percentages of Marines and Navy personnel but lower percentages of Army and Air Force personnel, more junior enlisted but fewer officers, and fewer college graduates. TMHED provides an unprecedented opportunity to study early psychiatric intervention in a combat zone and prospectively examines postdeployment health and career outcomes.