To confirm earlier studies of a high prevalence of coronary atherosclerosis in combat casualties of the Korean and Vietnam wars, we examined previously uncut coronary arteries from the hearts of 94 American male combat casualties (mean age, 20.5 years) from the Korean War using computerized planimetry and microscopic evaluation. Six (6.4%) men had severe atherosclerosis (75% to 90% cross-sectional area luminal narrowing) in one or more coronary arteries; five of the six had fibrous plaques, and one had a complicated plaque. Our prevalence is similar to that reported previously (5%). Therefore, to determine whether the decrease in the incidence of severe coronary atherosclerosis today is the result of decreased plaque formation in the young, we will need to examine at least 772 men to detect a 50% decline with 85% to 90% confidence.