Sudden death among military recruits is a rare but devastating occurrence. Because extensive medical data are available on this cross-sectional and diverse population, identification of the underlying causes of sudden death may promote health care policy to reduce the incidence of sudden death.

To determine the causes of nontraumatic sudden death among a cohort of military recruits.

Retrospective cohort study using demographic and autopsy data from the Department of Defense Recruit Mortality Registry.

Basic military training.

All nontraumatic sudden deaths from a monitored 6.3 million men and women age 18 to 35 years.

Descriptive analysis, crude mortality rates of causes of sudden death, and frequency of events as a function of cause of death.

Of 126 nontraumatic sudden deaths (rate, 13.0/100 000 recruit-years), 108 (86%) were related to exercise. The most common cause of sudden death was an identifiable cardiac abnormality (64 of 126 recruits [51%]); however, a substantial number of deaths remained unexplained (44 of 126 recruits [35%]). The predominant structural cardiac abnormalities were coronary artery abnormalities (39 of 64 recruits [61%]), myocarditis (13 of 64 recruits [20%]), and hypertrophic cardiomyopathy (8 of 64 recruits [13%]). An anomalous coronary artery accounted for one third (21 of 64 recruits) of the cases in this cohort, and, in each, the left coronary artery arose from the right (anterior) sinus of Valsalva, coursing between the pulmonary artery and aorta.

This cohort underwent a preenlistment screening program that included history and physical examination; this may have altered outcomes.

Cardiac abnormalities are the leading identifiable cause of sudden death among military recruits; however, more than one third of sudden deaths remain unexplained after detailed medical investigation.