The invention relates to a method for increasing the toughness and/or stiffness of bone and/or reducing the likelihood and/or severity of bone fracture by administering a parathyroid hormone. The method can be employed to increase toughness or stiffness of bone at a site of a potential or actual trauma, such as the hip or spine of a person at risk of or suffering from osteoporosis. The method of the invention can reduce the incidence of vertebral fracure, reduce the incidence of multiple vertebral fractures, reduce the severity of vertebral fracture, and/or reduce the incidence of non-vertebral fracture.