Nontraumatic deaths occur each year in organized high school and college athletics, resulting in considerable public concern. We conducted a study of the frequency and causes of nontraumatic sports deaths in high school and college athletes in the USA through the National Center for Catastrophic Sports Injury Research to define the magnitude of this problem and its causes. Over a 10-yr period, July 1983-June 1993, nontraumatic sports deaths were reported in 126 high school athletes (115 males and 11 females) and 34 college athletes (31 males and 3 females). Estimated death rates in male athletes were fivefold higher than in female athletes (7.47 vs 1.33 per million athletes per year, P < 0.0001), and twofold higher in male college athletes than in male high school athletes (14.50 vs 6.60 per million athletes per year, P < 0.0001). Cardiovascular conditions were more common causes of death than noncardiovascular conditions. Hypertrophic cardiomyopathy and congenital coronary artery anomalies were the most common causes of death. In high school and college athletes, males are at increased risk for nontraumatic sports deaths compared with females even after adjustment for participation frequency; college males are at greater risk than high school males. In all groups the deaths were primarily due to cardiovascular conditions.