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In the late 1990s, the U.S. Department of Defense (DoD) and Congress identified the need for coordinated epidemiological research to determine how military occupational exposures, including deployment, affect long-term health. The Institute of Medicine more specifically defined the importance of a large, prospective study for evaluating exposures and a broad spectrum of important health outcomes.

The Millennium Cohort Study was designed, in collaboration with all military services and the Department of Veterans Affairs (VA), to meet these research challenges.


The primary study objective is to evaluate the impacts of military service, including deployments and other occupational exposures, on long-term mental and physical health and health-related behaviors. The ultimate goal is to provide evidence-based knowledge products that inform and improve interventions, guidelines, and policies of key stakeholders including DoD and VA leaders.


Between 2001 and 2021, the Millennium Cohort Study has enrolled over a quarter of a million service members. The Cohort represents all service branches and components, including active duty, Reserve and National Guard members. Participants are asked to complete questionnaires every 3 to 5 years, regardless of service status. Participant follow-up is planned through at least 2068.


The survey includes measures such as demographics, medical symptoms and conditions, and health-related behaviors. In addition, validated instruments have been incorporated to capture physical and mental functional status, psychosocial assessments, post-traumatic stress, protective and risk factors, and occupational exposures. Information obtained from the survey is linked with other military databases, including data on deployment, occupation, vaccinations, health care utilization, disability, and VA health care records. In addition to revealing changes in service members’ and Veterans' health status over time, the Millennium Cohort Study serves as a resource that provides a solid foundation upon which a broad spectrum of epidemiological research may be constructed.


Over the last 20 years, our research has focused on military exposures and health outcomes, frequently in relation to deployments, other emerging health concerns, and the transition from military to civilian life. Research areas include:
  • Readiness and Deployment
  • Mental Health
  • Health-Related Behaviors
  • Occupational and Environmental Exposures
  • Physical Health and Injury Veterans Health
  • Financial Well-being, and Civilian Reintegration
  • Health Disparities


As the largest and longest-running cohort study in military history, the Millennium Cohort Study is uniquely positioned to follow the course of mental, physical, and behavioral health of service members, including the transition to civilian life. The Millennium Cohort Study is responsive to stakeholder requests for specific knowledge products. Findings from over 130 scientifi­c publications have informed and impacted numerous DoD and VA policies and guidelines.


Millennium Cohort Study research initiatives involve ongoing collaborations with partners from around the world. Collaborators include scientists, researchers, physicians, and other professionals from DoD, VA, and leading academic institutions. Additionally, the study collaborates with stakeholders by responding to their information requests and helping to identify priorities for programs and policies. Notable stakeholders include: DoD Office of Diversity, Equity, and Inclusion, DoD Psychological Center of Excellence, VA, DoD Sexual Assault Prevention and Response Office, and Defense Suicide Prevention   Of­fice.


The Principal Investigator of the Millennium Cohort Study is Dr. Rudy Rull, and the primary performing site is the Naval Health Research Center in San Diego, CA. The study team can be contacted (toll-free) at 1-888-942-5222 or email More information is also available on the website,

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