Background: Numerous studies document the health benefits of a physically active lifestyle, but relatively few document the hazards of physical activity. Because of the requirement for physical fitness to complete their mission, the United States military services have a vested interest in understanding the benefits and risks of physical activity including exercise and sports. One of these risks is injury. Rates and proportion of injuries caused by exercise- and sports-related (ESR) activities have not been reported previously across the services. Purpose: The purposes of this population survey were to (1) document the rates and proportion of all injuries caused by ESR activities among military personnel, (2) compare rates across the military services, and (3) describe the causes and types of ESR injuries as well as associated days of limited activity. Study Design: Descriptive epidemiology study. Methods: The Defense Manpower Data Center administered the web-based 2008 Status of Forces Survey of Active Duty Service Members to a random sample of active-duty personnel. In all, 10,692 servicemembers completed the survey, which included questions about injuries from any cause and from exercise and sports during the previous year. Responses were weighted to produce population estimates for injury rates (any injury and ESR injury). Percentage distributions were used to describe activities, injury types, days of limited activity, and contributing factors for ESR injuries. Results: There were 49% of servicemembers who sustained an injury from any cause in the previous year; 25% had an ESR injury. Thus, 52% of all injuries were ESR injuries. ESR injury rates ranged from 20% for the Navy to 33% for the Marine Corps. Running accounted for 45% of ESR injuries. Forty percent of ESR injuries were sprains and strains. As an indicator of injury severity, 35% of ESR injuries required more than 2 weeks of limited activity. Conclusion: This study quantified the overall incidence of injuries and the large proportion that are caused by exercise and sports among military personnel, a population of healthy, physically active adults. Prevention strategies should focus on running, weight training, basketball, and football. Recommendations include adherence to evidence-based practices to reduce the occurrence of ESR injuries.