The aim of our study was to assess the predictive value of the Singh index (SI), which estimates bone architecture, and bone density (BMD) when dealing with the mechanical competence of bone and to analze possible differences in bone properties between gender in humans. The relationship between SI, BMD, and mechanical competence was analyzed in 106 bone cylinders from 37 human femoral heads obtained during hip-joint replacement surgery for low energy fracture or for osteoarthritis. Bones from osteoporotic patients are less dense and more brittle compared with bones from osteoarthritic patients, as expected. Among osteoporotic patients female bones were more brittle than those from males, although BMD was similar. In osteoarthritic patients there were no significant differences among sexes. Bone mechanical competence varies according to BMD and to SI categories. Thus, our study suggests that bone strength is predicted by both BMD and bone architecture.