Patients with conversion disorder are often presented with critical symptoms or signs which could suggest severe organic disorders. Hysterical hemiparesis is a relatively rare presentation and it is difficult to diagnose because it is displayed as a unilateral motor weakness with or without sensory deficits. A previously healthy 23-years-old woman developed sudden onset of hemiplegia and hemianesthesia with loss of anal tone. Before the onset, she had a traffic accident. A through medical workup including X-rays, MRI, CT scans, EMG, and brain SPECT revealed no organic causes for such neurologic deficits. She gradually regained neurologic function over 2 months from the onset. Conversion disorder should be considered when symptom- related anatomic or physiologic abnormalities could not be proven with appropriate workup. Medical evaluation must be performed in advance to the diagnosis of conversion disorder to avoid misdiagnosis. (J Korean Acad Rehab Med 2009; 33: 357-360)