Twelve fractures of the femur occurred after irradiation in 12 patients during the past 15 years. All 12 patients had excision of a soft tissue sarcoma of the thigh. The periosteum was stripped in every case. The fractures had a deceptively innocuous radiographic appearance, which showed minimal comminution, displacement, and shortening. Treatment of the fractures was difficult and demanding. At a mean followup of 37 months, bony union was achieved in only four patients, and in all four cases union was delayed beyond 12 months. Because fracture healing typically is delayed, a loadsharing device such as an intramedullary nail may be preferable in treating these fractures. Primary or delayed bone grafting may be necessary, for no fracture united without bone graft. For elderly patients with low supracondylar fractures, primary endoprosthetic replacement may effect quicker rehabilitation. The possibility of local recurrence of tumor should be ruled out before definitive surgical treatment of the fracture. Closed, antegrade nailing in the presence of recurrent tumor may contaminate the flap for a salvage procedure such as hemipelvectomy and may compromise chances for cure.