In the late 1990s, in response to concerns about the health effects of deployments following the 1991 Gulf War, the Institute of Medicine and Congress identified the need to understand how military occupational exposures affected the long-term health of U.S. service members. The result was the Millennium Cohort Study, the largest prospective health study in Department of Defense history.

Designed in collaboration with all military services and the Department of Veterans Affairs, Millennium Cohort researchers evaluate detailed data from military occupational and deployment-related exposures as well as a broad spectrum of important health outcomes.


The Millennium Cohort Study contributes to force health protection by providing information critical for enhancing the long-term health of future generations of military members.

Although the original designers of the Study could not foresee the post-2001 military conflicts, this project is well-positioned to address health outcomes related to these operations. More than 61% of Millennium Cohort participants have deployed in support of the Global War on Terrorism.


  • Evaluate the impact of military service, including deployments and other occupational exposures, on the long-term physical, mental, behavioral, and functional health of service members.


Launched in the summer of 2001, the Millennium Cohort Study began enrolling a representative sample of U.S. military personnel, including both active duty and Reserve/Guard members. To date, over 201,000 Service members have enrolled in the cohort.

All participants provide important information on exposures and health through and beyond their time in service. The Millennium Cohort Study will follow participants through at least 2068.


  • Those who were currently deployed or had returned from deployment were more likely to report trouble sleeping compared with those who had not deployed.
  • Suicide risk was associated with depression, manic-depressive disorder, alcohol-related problems, and male gender, but not with deployment.
  • Physical activity was associated with decreased PTSD symptoms.
  • Deployment experiences and PTSD were not associated with unemployment among veterans.
  • Other key findings are available at: Millennium Cohort Study Publications.


  • Investigators include scientists from the Army, Navy, Air Force, Department of Veterans Affairs, and leading academic institutions.
  • The Millennium Cohort External Advisory Board includes many distinguished external scientific researchers and subject matter experts from academia, the DoD, and Veterans Affairs as well as leading Veteran Service Organizations.
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