Acetabular fractures due to bone insufficiency are rare and difficult to diagnose based on clinical findings alone. Plain films are often normal for a long period of time. We report two cases of acetabular fractures in women aged 78 and 90 years, respectively. An acetabular fracture should be considered in elderly females with sudden onset of pain in the groin occurring immediately upon weight-bearing, a clinostatic syndrome, and increased radionuclide uptake by the acetabulum. Computed tomography and magnetic resonance imaging are useful when the diagnosis remains in doubt.