Injuries are a common occurrence in young, active civilian and military populations. This study examined injury incidence and the association of musculoskeletal injuries with age and physical fitness in soldiers. Subjects were a cohort of 298 male soldiers assigned to an infantry battalion in Alaska. The soldiers' ages were obtained from the battalion records and their physical fitness was assessed from 2-mile run times, sit-ups, and push-ups. Injuries were documented from a retrospective review of the soldiers' medical records for a 6-month period (October to March) before the fitness testing. Fifty-one percent of the soldiers suffered one or more injuries. The most common injury diagnosis was musculoskeletal pain, followed by strains, sprains, and cold-related injuries. Soldiers experienced a total of 212 separate injuries, which resulted in 1764 days of limited duty. The crude annualized injury rate was 142 injuries per 100 soldiers (one soldier could experience more than one type of injury). The proportion of soldiers injured decreased as age increased. Slower 2-mile run times and fewer sit-ups were associated with a higher incidence of musculoskeletal injuries. This study documents the injury incidence in infantry soldiers and identifies younger age and low physical fitness as potential risk factors for these injuries.