Musculoskeletal injuries occur frequently in connection with physical activity. More information was sought on pretraining factors that may predispose to such injuries. Data were obtained on the age, height, weight, aerobic fitness as measured by a 3000-m run test, and health as assessed on the basis of a medical examination, of 912 male conscripts prior to an 8-week period of basic military and physical training. Injuries were registered as they occurred by doctors attached to the training camp. Every fourth to fifth conscript suffered one or more musculo-skeletal injuries during basic training. Achilles tendinitis, low back pain, periostitis or compartment syndromes, and overuse knee injuries were the most frequent diagnosis groups. In 74% of the injuries, a tentative cause was related to organized service activities. According to univariate analyses, risk factors were age over 23 years, high body mass index (BMI), slow run times and dysfunctions of the back or lower limbs. A lower classification of mental health, but not dysfunctions of the lower limbs, was an additional risk factor if only injuries with causes connected with organized service activities were considered. Height and weight were not associated with injuries. In multiple logistic regression analysis, age and 3000-m run times were masked by correction for BMI, while BMI, dysfunctions of the back and lower limbs, and reduced mental health showed the same significance as in the univariate analyses.