Rapidly-progressive spontaneous progression of the osteolysis following internal fixation of pathological fracture in patients with Paget's disease has not been previously reported. We describe two patients, aged 59 and 65 years, respectively, who had pathological subtrochanteric fractures in Pagetic femora fixed internally using an interlocked intramedullary nail, and who developed spontaneous rapid osteolysis. Both patients responded favourably to long-term treatment with alendronate, with resultant fracture union and resolution of osteolysis.