A 67 year-old woman referred to our Metabolic Bone Diseases Outpatient Clinic for non-traumatic left thigh pain occurring in the last few weeks. She had been diagnosed with osteoporosis in 2004 and was treated with oral bisphosphonates (alendronate 70 mg weekly for the first four years and then with risedronate 35 mg weekly until the day she came to our attention) and vitamin D (cholecalciferol 25000 IU monthly). Her bone densitometry showed, according to the World Health Organization classification, a T-score in the osteoporosis range (−2.7 SD at femoral neck, −3.0 SD at lumbar spine).