BACKGROUND: Subtrochanteric insufficiency fractures in post-menopausal patients have not been commonly reported in the literature. A recent increase in the incidence of such fractures occurring in patients while on alendronate therapy led us to conduct a retrospective review of these patients in our institution. METHODS: Seventeen patients, with a mean age of 66 years, sustained low energy subtrochanteric fractures within a 20-month period. These patients were incidentally found to be on alendronate therapy for an average of 4.8 years. Clinical data and history were reviewed and roentgenograms were evaluated by a single investigator. All additional imaging and bone mineral density measurements available were analysed. RESULTS: A characteristic fracture configuration suggestive of an insufficiency stress fracture was identified on plain radiographs. This consisted of (a) cortical thickening in the lateral side of the subtrochanteric region, (b) a transverse fracture, and (c) a medial cortical spike. In addition, 9 (53%) patients had bilateral findings of stress reactions or fractures, and 13 (76%) had symptoms of prodromal pain. CONCLUSIONS: These insufficiency fractures could possibly have developed from the over suppression of bone turnover from prolonged alendronate therapy, in keeping with recently published evidence. This study further highlights the need for heightened awareness of alendronate's potential adverse effects.