During a period of forty months when 5,400 total hip arthroplasties were performed at the Mayo Clinic, ten patients (nine operated on at this clinic and one elsewhere) were seen with fractures that occurred four to twenty months after operation: three in the pubis, six in the proximal one-third of the femur, and one, a combined acetabular and femoral fracture. Two of the pubic fractures were typical stress fractures; the others were caused by recognizable trauma. Defects in the femoral cortex (screw holes and misdirected reaming) or an inadequate amount and distribution of cement about the top of the femoral stem seemed to predispose to femoral fracture. Fracture healing did not appear to be adversely affected by the presence of the prosthesis or the methylmethacrylate. Open reduction was used only when adequate apposition and alignment was not achieved by closed methods (traction and a spica cast). The pubic fractures required no treatment.