Spontaneous or pathologic fractures are those that occur in the absence of trauma sufficient to disrupt the integrity of normal bone. Spontaneous fractures can be thought of as opportunistic fractures since they occur in bones that are weakened, for example, by tumors, nutritional or metabolic abnormalities, or prior injury (e.g., fracture, surgical repair). In an otherwise healthy adult, a spontaneous fracture can occur as an unusual manifestation of the adaptive process of bone remodeling in response to changes in physical activity (stress fractures). For centuries, spontaneous fractures, particularly of the lower extremities, have threatened the health and effectiveness of military forces, particularly during recruit training. This report summarizes recent experiences regarding spontaneous fractures of the femur among trainees at Fort Leonard Wood, Missouri, and Armywide.