Specimens of femoral cortical bone from eighteen subjects between two and forty-eight years old were loaded in bending. Compared with the bone of adults, that of children had a lower modulus of elasticity, a lower bending strength, and a lower ash content. However, the children’s bone deflected more and absorbed more energy before breaking. It also tended to absorb more energy after fracture had started. The typical greenstick fracture surface of many specimens of children’s bone requires more energy for its production than the relatively smooth surface of adult specimens.