The occurrence of stress fractures (SF) in 1,118 Israeli conscripted infantry recruits and their relation to the pre-army physical fitness as estimated from the results of a competitive field run were studied prospectively. About 8.5% of recruits sustained scintigraphy-proven SF during their basic training. The pre-army physical fitness of recruits who sustained SF was not significantly different from that of recruits who did not. Tibial SF accounted for 57% of the total, metatarsal for 22.4%, and femoral for 17.9%. Other anatomical locations were rare Twenty-eight of 35 (80%) femoral SF were asymptomatic. There were no cases of displaced SF at any site. Only one recruit had to discontinue training because of SF. Our data suggest that diminished pre-army physical fitness does not predispose recruits to SF, and that most scintigraphy-defined SF in conscripted infantry recruits are benign.