Flexion and extension lateral radiographs of the cervical spine may suggest signs of ligamentous and soft tissue injuries in a potentially unstable spine. However, patients with acute injuries and severe pain and muscle spasms may not be able to move their necks effectively, severely compromising the diagnostic yield of the radiographs. In addition, there are reports of serious neurologic injuries occurring with the use of these radiographs in acutely injured patients. The purpose of this study was to determine the effectiveness and yield of obtaining cervical spine flexion and extension radiographs in the emergency department on acutely injured patients. Review of all patients with cervical flexion and extension radiographs presenting to a Level 1 trauma center was performed. All radiographs were judged based on the adequacy of flexion and extension movement and positive findings indicative of instability by the radiologist in the emergency room. The radiographs of one patient (0.34%) revealed positive findings of instability. Of the 290 flexion and extension radiographs, 97 (33.5%) of them showed such little or inadequate flexion or extension movement that cervical stability could not be assessed. Flexion and extension cervical radiographs should not be obtained routinely in the emergency department because 1/3 of these studies will be inadequate because of pain and muscle spasms experienced by patients. Patients with cervical injuries may not be able to fully flex and extend their necks; this may lead to false reassurance to patients who actually have had an inadequate study to diagnose potential instability.