The incidence and nature of exertion-related injuries were studied at a South African Defence Force basic training centre. A total of 404 separate injuries were sustained by 359 of 947 recruits during the 10-week basic training cycle. Of these injuries, 18,3% were sustained with (group 1) and 81,7% without (group 2) an obvious sudden precipitating event. Exertion-related injuries were responsible for a loss of 2711 recruit-days of basic training. While the knee sustained the largest number of group 2 injuries, lower leg trauma resulted in the greatest loss of basic training time. Forty-two separate radio-graphically confirmed stress fractures were incurred by 39 recruits, an incidence of 4,12%, which is considerably higher than that in the US Army. These data leave little doubt that the present training programme is costly in terms of training-time lost and may prevent large numbers of recruits from deriving the optimum conditioning benefits.