Fractures of the proximal femur in elderly individuals are becoming increasingly common in the industrialized world and represent a heavy burden in both socioeconomic and human terms. Two factors are key to the pathophysiology of these fractures: falls and decreased bone strength due to osteoporosis. Femoral and vertebral bone density was measured in 40 elderly women (83 +/- 5 years) who experienced a fall; in those who developed a femoral fracture as a result of the fall, femoral bone density was lower by 12 to 21% (z score: -0.7 to -1.04) than in those with no fracture, after adjustment for age, height and weight. Femoral neck and trochanteric area measurements had the best predictive value (area under the RoC curve: 75% +/- 8%). These was no difference by anatomic fracture type (neck or trochanter). Patients with pertrochanteric fractures had lower vertebral bone densities than controls. These findings, together with recent prospective data, demonstrate that in addition to falls, bone loss (osteoporosis) promotes the occurrence of fractures of the proximal femur in elderly patients. This has important practical implications for the detection and prevention of these fractures.