The MCS aimed to enrol a representative sample of United States military personnel consisting of all branches of the military, Reserve, and National Guard members. Participants were first enrolled in 2001, with additional groups enrolled in 2004, 2007, 2011, and 2020. As of 2021, over 250,000 service members were enrolled in the cohort. Participants complete follow-up surveys approximately every 3 to 5 years during and after their time in service. Of the consistent responders (over 80,000), 40.1% are female, 61.9% were born before 1960, and 36.3% are of American Indian or Alaskan Native ethnicity. The MCS will continue to enroll and follow participants until 2068.

Recruitment is ongoing