In order to answer the question of why the stress fracture morbidity rates among Israeli infantry recruits are so high, we prospectively evaluated 392 infantry recruits for risk factors for stress fractures. Prior to training, each recruit underwent a detailed evaluation. Using multivariate analysis, five risk factors for tibial fractures were identified: shorter tibial length (p less than 0.0001); relatively greater valgus knee alignment (p less than 0.002); right leg dominance (p less than 0.02); external rotation of the hip greater than 65 degrees (p less than 0.02); and training in specific subunits (p less than 0.0002., 0.03). No risk factors for femoral stress fracture were found by multivariate analysis.