A retrospective case-control study into the risk factors for injury during basic military training was conducted at the Recruit Training Unit, Royal Australian Air Force Base Edinburgh, South Australia. Case subjects were recruits suffering a musculoskeletal injury during the course, severe enough to result in backcoursing (being delayed and joining a later course) and usually requiring the loss of 5 days of training. Control subjects were 629 recruits selected randomly from recruits who were not case subjects from the same period of Jan 1, 1985 to Dec 31, 1990. Two hundred thirty-eight cases were identified (2.7% of the recruit population), of which 123 were overuse-type injuries and 115 acute-type injuries. Most injuries occurred in the first 2 weeks of training. Bivariate and logistic regression analysis of possible risk factors for injury was conducted, both for all case subjects and for the subgroup of case subjects with overuse injuries. Statistically significant associations were identified for female gender, body mass index > 26.9, winter training, a history of lower limb injury, and the presence of a lower limb deformity. All these associations were stronger for overuse injury, and preenlistment physical activity was also significantly associated with overuse injury. No significant association was found for height, weight, age, smoking, or gender makeup of courses. Most striking was a large rise in overuse injury incidence in women over the period of study, from 0.2% in 1985 to 8.8% in 1990. Reasons for this increase may include "social pathogenesis."