U.S. Army soldiers lose substantial training hours as a result of musculoskeletal injuries. Most military injury data have focused on basic trainee populations. This study examines activities associated with injuries in operational infantry soldiers. We conducted a randomized, retrospective medical record review of 339 records from a total of 3,195 light infantry soldiers over 13 months. The annualized incidence of injuries was 95 per 100 soldiers per year vs. 74 per 100 for illness. There were 372 injuries, representing 56% of sick-call diagnoses. Physical training caused 50% of all injuries, and 30% of those were linked to running. Injuries caused nearly 10 times the number of limited duty days as illness. Soldiers with lower extremity running injuries spent seven times more days on profile than those with nonrunning injuries. We conclude that physical training is related to a high number of injuries in infantry soldiers. This study provides important data on activities and injuries in operational infantry soldiers.