BACKGROUND: Reports of atypical femur fracture in bisphosphonate-exposed women have prompted interest in characterizing the clinical profiles of these patients. METHODS: Among women age >/=60 years with hip or femur fracture during 2007-2008, we identified 79 with low-trauma subtrochanteric or femoral shaft fracture. Radiographic images were reviewed to assign fracture pattern and distinguish atypical femur fracture from non-atypical femur fracture. Differences in clinical characteristics and pharmacologic exposures were compared. RESULTS: Among 79 women (38 subtrochanteric and 41 femoral shaft fracture), 38 had an atypical femur fracture. Compared to those with a non-atypical femur fracture, women with atypical femur fracture were significantly younger (74.0 vs 81.0 years), more likely to be Asian (50.0 vs 2.4%) and to have received bisphosphonate therapy (97.4 vs 41.5%). Similarly, the contralateral femur showed a stress or complete fracture in 39.5% of atypical femur fractures vs 2.4% non-atypical femur fracture, and focal cortical hypertrophy of the contralateral femur in an additional 21.1% of atypical cases. CONCLUSIONS: Women suffering atypical femur fractures have a markedly different clinical profile from those sustaining typical fractures. Women with atypical femur fracture tend to be younger, Asian, and bisphosphonate-exposed. The high frequency of contralateral femur findings suggests a generalized process.