Although fragility fractures in the subtrochanteric/femoral shaft (ST/FS) regions are not frequently reported in osteoporotic individuals, a potential link between prolonged bisphosphonate use and low-energy femoral fractures resulting from suppression of bone turnover, accumulation of micro-damage, and failure of aging collagen1. Such fractures have been characterized by a specific radiographic appearance2, a simple transverse or oblique fracture, beaking of the cortex, and diffuse cortical thickening3,4,5. We performed retrospective chart reviews on 10 women with ST/FS fractures (mean age 69.2, SD 8.9, yrs), all of whom were undergoing longterm alendronate therapy (mean 8.3, SD 2.4, yrs). Two patients had bilateral fractures. All fractures met the American Society for Bone and Mineral Research criteria for atypical femoral fractures2. Five women had thigh pain prior to fracture, 4 had a previous fragility fracture, and 5 of the 8 patients that underwent investigations on the contralateral femur had stress reactions (Figure 1). All fractures were transverse or short oblique in configuration, without comminution, and showed diffuse or focal cortical thickening. Radiographs were analyzed by a musculoskeletal radiologist to quantify total (medial + lateral) cortical thickness at a fixed location (Figure 2). The mean ratio of cortical thickness normalized to bone diameter to correct for magnification was 0.50 (SD 0.09). It is unclear if these atypical fractures are related to altered bone physiology or excessive stresses. Cortical thickening may be a sequela of gradual periosteal and endosteal new bone formation, secondary to cortical fractures and cumulative stress reaction. Future studies quantifying cortical thickness in individuals without femoral fractures would provide reference values for comparison.