title: Millennium Cohort: enrollment begins a 21-year contribution to understanding the impact of military service.
abstract: OBJECTIVE
  In response to health concerns of military members about deployment and other service-related exposures, the Department of Defense (DoD) initiated the largest prospective study ever undertaken in the U.S. military.
  
  
  METHODS
  The Millennium Cohort uses a phased enrollment strategy to eventually include more than 100,000 U.S. service members who will be followed up through the year 2022, even after leaving military service. Subjects will be linked to DoD and Veterans Affairs databases and surveyed every 3 years to obtain objective and self-reported data on exposures and health outcomes.
  
  
  RESULTS
  The first enrollment phase was completed in July 2003 and resulted in 77,047 consenting participants, well representative of both active-duty and Reserve/Guard forces. This report documents the baseline characteristics of these Cohort members, describes traditional, postal, and Web-based enrollment methods; and describes the unique challenges of enrolling, retaining, and following such a large Cohort.
  
  
  CONCLUSIONS
  The Millennium Cohort was successfully launched and is becoming especially relevant, given current deployment and exposure concerns. The Cohort is representative of the U.S. military and promises to provide new insight into the long-term effects of military occupations on health for years to come.
authors.affiliation: Department of Defense Center for Deployment Health Research, Naval Health Research Center, P.O. Box 85122, San Diego, CA 92186-5122, USA. ryan@nhrc.navy.mil
authors.forename: Margaret A K
authors.initials: MA
authors.lastname: Ryan
authors.forename: Tyler C
authors.initials: TC
authors.lastname: Smith
authors.forename: Besa
authors.initials: B
authors.lastname: Smith
authors.forename: Paul
authors.initials: P
authors.lastname: Amoroso
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Boyko
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Gray
authors.forename: Gary D
authors.initials: GD
authors.lastname: Gackstetter
authors.forename: James R
authors.initials: JR
authors.lastname: Riddle
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Wells
authors.forename: Gia
authors.initials: G
authors.lastname: Gumbs
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Corbeil
authors.forename: Tomoko I
authors.initials: TI
authors.lastname: Hooper
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D003365:Costs and Cost Analysis; D005260:Female; D017144:Focus Groups; D006304:Health Status; D006801:Humans; D020407:Internet; D008297:Male; D008887:Military Medicine; D008889:Military Personnel; D018579:Patient Selection; D010865:Pilot Projects; D011786:Quality Control; D011795:Surveys and Questionnaires; D014481:United States; D014728:Veterans