Frequently Asked Questions

Frequently Asked Questions

Below you'll find answers to commonly asked questions about the Millennium Cohort Study (MCS). You can either browse by topic area or use the search box to find specific information.

If you still can't find the answer you're looking for, just contact us at [email protected] or (888) 942-5222!

Program Information
Why was this study created and by what authority?

In the late 1990s, public concern about the potential health effects of deployments following the Vietnam and Gulf War conflicts prompted the Institute of Medicine, Department of Defense (DoD), Veteran’s Affairs (VA), and Congress to identify how military occupational exposures affected the long-term health of U.S. service members. The 1999 National Defense Authorization Act (NDAA), Section 743, established “a longitudinal study to evaluate data on the health conditions of members of the armed forces upon their return from deployment.” The result was the Millennium Cohort Study (MCS), the largest prospective health study in DoD history.

This DoD-sponsored project is conducted at the Naval Health Research Center (NHRC) in San Diego, CA.

Report Control Symbol #DD-HA(AR)2106
Office of Management and Budget Approval #0720-0029
Primary Institutional Review Board Protocol #NHRC.2000.0007

Why is the Millennium Cohort Study (MCS) being conducted, and what is a cohort study?

A cohort study follows a distinct group of people over an extended period of time. In epidemiological research, only a cohort study has the strength to describe long-term health outcomes that are of concern to the military.

The Department of Defense determined a need to collect data to evaluate the health of service members throughout their military careers and after leaving military service. Important health facts, which may seem obvious now, were not always known to be true - they were learned through cohort studies. For example, we know that smoking causes lung cancer and that untreated high blood pressure causes heart disease. But less than 50 years ago, these relationships were not clear.

What does joining the MCS involve?

Joining the MCS involves signing two forms (an informed consent and HIPAA Authorization) and completing one survey (via mail or online) approximately every three years.

Do I have to visit my doctor or give a blood sample?

Your participation does not involve doctor visits or collecting blood samples or other biological specimens. In the future, you may be invited to join new studies that do request this information. Participation in any of these other studies is strictly voluntary. You will have the option to decline participation in these potential studies; this will not affect your participation in the Millennium Cohort Study.

How are my survey answers used?

MCS researchers, in collaboration with all military services and the VA, use survey data to evaluate how military occupational and deployment-related exposures influence a broad spectrum of important health outcomes.

Although the original designers of the study could not foresee the military conflicts occurring following the events of September 11, 2001, the study was uniquely positioned to examine near- and long-term effects related to these operations. As force health protection continues to be a priority for the United States military, the study will inform the short- and long-term health for generations of military members.

Do I have to answer all of the survey questions?

While every response is incredibly valuable in our study, you do not have to answer all survey questions. Participants always have the option to skip questions and leave them blank.

Why do you ask the same question twice or more in the same survey?

While a few of the questions on our survey may seem repetitive or duplicate previous questions, we assure you that each item has a very specific purpose.

What happens if I start a survey but cannot finish it?

Each survey cycle opens and closes on specific dates. Once the survey cycle is open, we invite participants to visit our website and fill out their survey. If you are unable to finish the survey all at once, that is okay! Our website uses cookies that recall the last page that you were on and allows you to continue where you left off at a later time.

How do I withdraw from the MCS?

If you wish to withdraw from the MCS, please email or call us stating your request to be removed from the study. After we verify your identity, you will receive an email confirming your removal from the study.

I am currently deployed/unavailable to complete a survey. How can I continue to participate?

If you are currently deployed, you can still participate! If you are completely unavailable (e.g., no internet access and not returning home soon) you may still participate in our next survey cycle. Please reach out to the study team so that we can remove you from our reminders until the next survey.

I have missed a survey/several surveys. Can I still participate?

Yes! If the window for the current survey cycle is still open, then yes you can still participate! However, if the current survey cycle is closed, then you may have to wait till the next survey cycle is open to participate. Even if you haven’t responded to every questionnaire, any information that you provide is very useful.

How often will I have to submit a survey?

You will be asked to complete one survey, online or through the mail, at least every three years until 2068.

What if I move, have a new email address, or change my name?

If you move or change duty stations, obtain a new email address, or need to update your name, we ask that you contact us via email or phone to let us know your new contact information.

Email: [email protected]
Phone: 1 (888) 942-5222
DSN: 553-7465

Can I participate even though I was not invited?

No, only those who receive invitations are allowed to participate. The scientific validity of this study requires study investigators to follow a specific enrollment protocol. A random sampling process is used to identify a population of service members to whom invitations are sent.

Do any other factors affect my ability to join/remain in the MCS?

As long as you were invited to join the project and you provided your consent, you may join.

Veterans commonly ask if they can/should remain involved after they leave service. The answer is YES! No matter how long you served in the Armed Forces, it is important to recognize that the study is intended to continue to follow participants even after you leave military service.

Can I still join the MCS if I don’t want to sign the informed consent or provide HIPAA Authorization?

The informed consent is required to participate in the Millennium Cohort Study.

However, if you do not feel comfortable providing HIPAA Authorization, you still have the option to remain involved as a participant in the Millennium Cohort Study. While you will still be able to participate and complete your surveys, we will not request your health information from the Military Health System.

I am perfectly healthy and/or have no health issues – how will joining the program be helpful?

The MCS aims to capture any long-term health issues that may occur over a lifetime. Even though you may not currently be experiencing any health issues your involvement in this study is very important.

We would like to follow your health over time so that way if you happen to have a health issue down the line (such as when you are older), we would like to see if it has any relevance to your military experience. For example, the long-lasting health effects related to smoking are now understood because of research that followed the health of large groups of smokers and non-smokers.

I have never deployed – how will joining the program be helpful?

Even if you never deployed, your participation is still valuable to the Millennium Cohort Study. As the objective of the study is to understand the effects of deployment on long-term health, it is important to have input from those that never deployed. This allows us to make comparisons with those who deployed during their military career. Your participation in the study will help define healthcare policy for future generations of military personnel, guide prevention and treatment programs, and create stronger opportunities for former, current, and future service members.

I received an email, postcard, or survey but have since separated from the military, can I still take part?

Absolutely! We need your continued participation even if you are no longer serving in the military. Currently, over 50% of the Cohort has left military service. The Millennium Cohort Study is designed to research the effects military service may have on service members' health over a period of many years, including after military service is complete.

The Science
Will I receive my results?

As a population-based research study, individualized results will not be made available. Rather, analyzed data from multiple participants are summarized and reported in our research publications. This study website is regularly updated with the information from published manuscripts and provides a description of the specific research results from each manuscript. A link to the full paper or abstract is also provided should you want a copy of the published article.

Will the MCS tell me if something is wrong with me?

No. This is a population-based research study and data collected will not be shared with healthcare providers or used to make decisions about treatment that any individual should receive. If you feel that you might need medical care or counseling, you should contact the appropriate health care personnel.

Where can I find our more information about the scientific results from the MCS?

All MCS publications are posted to the Publications page of our website:

We have over 150 publications, so you may find it helpful to use the search box feature to find specific topics of interest. You can also bookmark the page if you wish to stay up to date with our latest research, as we do have other reports undergoing review that will be posted to the website upon publication.

You can also find summarized research briefs at:

Disabled and Special Needs
I have a disability or special need. Can someone help me fill out the survey?

Please contact the study team for more information. The study team can be reached by email at: [email protected] or by phone at: (888) 942-5222 or DSN: 553-7465

Data Security and Storage
Why does this project use a .org (rather than .mil) website?

The Millennium Cohort Study website address ( uses a .org domain name for complex logistic reasons. It is important to recognize that the study is intended to continue to follow participants even after they leave military service. The project is anticipated to remain DoD-led as well as sponsored, yet it must retain an identity that includes both military and non-military components. For this reason, as well as other technical considerations, the Millennium Cohort Study website is hosted on a .org address. The study team recognizes that .mil websites are more clearly recognizable as authorized DoD sites. All participants should be assured, however, that all Millennium Cohort information security standards meet or exceed those required by DoD websites.

What happens to the survey information I provide?

Paper records and computer files are maintained securely in accordance with current DoD regulations. All study data, including but not limited to survey data, data extracted or received from DHA and DoD sources, and data from non-DHA and DoD agencies or institutions, are stored and analyzed on access-controlled folders on a secure Naval Health Research Center network drive only accessible by approved study staff. Access to areas where records are maintained is limited to authorized study personnel and access to data is provided on a need-to-know basis only.

How does the MCS access my health records and what do you do with them?

We do not have direct access to your health records; however, if you provided HIPAA authorization, we do request and receive pieces of medical data from the Military Health System (MHS). We link these data with your survey responses to form a more complete picture of your overall health. This combined information is then analyzed to evaluate the impacts that military deployment, military occupations and exposures, and general military service may have had on the long-term health of service members and veterans.

Does the MCS only access military health records?

No. To keep the survey as short as possible, we request data from other sources and databases to aid in forming a more complete picture of your overall health. We may connect your survey data with other databases, medical records, surveys, or biological specimens collected or maintained by the Department of Defense, Department of Veterans Affairs, federal or state agencies, or nongovernmental organizations such as the National Student Clearinghouse.

Confidentiality, Privacy, and Security
Are there risks to participation?

The study team understands the sensitivity of health-related information. Strict confidentiality of all data on participants is maintained. Data will not be shared with military commands, disability evaluators, insurance companies, or anyone not directly involved in data analysis.

All data are maintained securely. Only summary information from the entire cohort, with no identifying information, will be shared.

How safe is my information?

Very secure. The information you provide on your questionnaire is protected and stored in conjunction with a Subject ID number and nothing that would link it to your identity. Only Millennium Cohort Study researchers have access to the data. No personal identifying data will ever be released. All information is stored in locked filing cabinets in double locked rooms on United States Government property as well as additional safeguards for Web-related data. Information stored on computers is protected by all measures required by DoD computer security regulations. Additionally, information on individuals cannot be obtained through FOIA requests, and your insurance companies will not have access to any information that you provide us.

Can MCS guarantee confidentiality and privacy are protected?

Our participants’ privacy and confidentiality are one of our highest priorities. We have certain protocols set in place to ensure the confidentiality and privacy of your information. This includes obtaining a certificate of confidentiality as well as only allowing a select group of DoD and IRB (Institutional Review Board) approved investigators to access your data. Furthermore, all data that personally identifies you is removed before research analyses are performed.

What is a Certificate of Confidentiality?

A Certificate of Confidentiality is a document from the National Institutes of Health which allows the MCS team to refuse to disclose information (for example, if there was a court subpoena) that may identify you in any federal, state, or local, civil, criminal, administrative, legislative, or other proceedings. This means that if someone (police, courts, relatives, etc.) wants access to your information, the MCS team has the right to refuse access to your data.

Can insurance companies or employers find out about the results of this research?

Insurance companies will not have access to your survey data. Survey responses do not become part of participants' service or medical records, and cannot be used for healthcare, administrative, or benefits purposes. The consent form details these protections, and all approval authorities require such protections. Please rest assured that our participants’ privacy continues to be our highest priority.

What happens to my information if I pass away?

In the unfortunate event that you pass away, your information will be retained by the MCS team and remain strictly confidential (meaning that only DoD approved researchers, like the MCS team, can access it).

Can relatives get access to my information?

Your relatives will not have any access to your information. Access to data is provided on a need-to-know basis only and examined by DoD approved researchers (contractors, military, and government employees), all of whom have met applicable security and privacy training requirements. In no cases will your protected personal data ever be intentionally released.

Accessing Your Records
How do I get a copy of my military records, medical records, or my DD214?

You can use the Defense Personnel Records Information Retrieval System to request and receive scanned copies of documents in your Official Military Personnel File (OMPF).

For OMPF records not available in milConnect, military veteran health records, or for records requests from a veteran's next of kin or a member of the public, please visit the National Archives - National Personnel Record Center, Military Personnel Records for assistance:

Service Records and DD214:

Medical Records:

Can I get a copy of my completed survey(s)?

To request a copy of your completed survey, email the study team at: usn.nh[email protected]

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