We identified 215 exercise-related deaths in U.S. military personnel on active duty during 1996-1999. The most complete case information was for active duty Army personnel during 1998-1999, providing an exercise-related death rate of 4.3 per 100,000 person-years (41/963,000) and accounting for 6% of Army deaths (14 during physical fitness testing). The cause of death was confirmed by autopsy or clinical data for 85% of the cases. Arteriosclerotic coronary artery disease was the predominant cause of death for those 30 to 58 years of age. For age 17 to 34 years, 50% of deaths were attributable to preexisting heart disease (16% from coronary anomalies), 20% attributable to nontraumatic drowning, and 12% attributable to exertional heat illness, also a potential contributory factor in cardiac deaths. Most exercise-related deaths were related to running (60%), sports (14%), and swimming (13%). Improvements in health promotion, medical management, and stricter exclusion from inappropriate exercise (especially fitness test runs) could reduce these deaths.