We reviewed the clinical and autopsy records of the 19 sudden cardiac deaths that occurred among the 1 606 167 US Air Force healthy, medically screened recruits (90% male; 17 to 28 years old) during a 42-day basic training period between 1965 and 1985. Sixteen (all male) died suddenly of underlying structural heart disease, whereas no anatomic cause of death was identified in the remaining three. Thirty-two nonsudden, noncardiac deaths occurred during the same period, and only two had structural heart disease. Strenuous physical exertion was associated with sudden death in 17 of 19 cases (0.017 deaths per 50 000 exercise-hours), and the most frequent underlying etiology was myocarditis. Sudden cardiac death, a rare event in healthy young adults, is usually associated with exertion.