Atypical femoral fractures (AFF) are uncommon, but catastrophic, complications of the anti-osteoporosis medications, bisphosphonates. We aim to identify patients either protected from, or at risk of, AFF by identifying changes in their bone geometry, structure and quality, and genes increasing risk of these fractures. In this way, these cheap and effective anti-osteoporosis treatments can be targeted to patients at the lowest risk of AFF and alternative treatments to those at highest risk.