Background: Sudden cardiac death associated with physical exertion (SCD/E) is a complicated pathophysiological event. This study aims to calculate the incidence rate of SCD/E in the US military population from 2005 to 2010, to characterise the demographic and cardiovascular risk profiles of decedents, and to evaluate aetiologies of and circumstances surrounding the deaths. Methods: Perimortem and other relevant data were collected from the Armed Forces Medical Examiners Tracking System, Armed Forces Health Longitudinal Technology Application, and Defense Medical Epidemiology Database for decedents meeting SCD/E case definition. Incidence rates were calculated and compared using negative binomial regression. Results: The incidence of SCD/E in the Active Component (ie, full-time active duty) US military from 2005 to 2010 was 1.63 per 100 000 person-years (py):0.98 and 3.84 per 100 000 py in those aged <35 and ≥35 years, respectively. Atherosclerotic cardiovascular disease was the leading cause of death overall (55%) and in the ≥35-year age group (78%), whereas the leading cause of death in the <35-year age group (31%) could not be precisely determined and was termed idiopathic SCD/E (iSCD/E). SCD/E was more common in males than females (incidence rate ratio (IRR) = 5.28, 95% CI 2.16 to 12.93) and more common in blacks than whites (IRR=2.60, 95% CI 1.81 to 3.72). All female cases were black. Conclusions: From 2005 to 2010, the incidence of SCD/E in US military members aged <35 years was similar to most reported corresponding civilian SCD rates. However, the leading cause of death was iSCD/E and not cardiomyopathy. Improved surveillance and agebased prevention strategies may reduce these rates.