Children with herpes simplex virus encephalitis have a relapse in approximately 25% of cases, which rarely may present as a movement disorder, most often choreoathetosis. The anatomic basis for herpes simplex virus encephalitis-associated movement disorders has been poorly understood, because neuroimaging, to date, has not been able to show the direct involvement of the areas of the brain that typically govern such movements. We present a patient with abnormal involuntary movements after herpes simplex virus encephalitis, with new lesions on MRI between the time of initial presentation and the development of choreoathetosis. To our knowledge, this is the first patient with a post-herpes simplex virus encephalitis movement disorder with neuroradiographic evidence of thalamic involvement correlating with the onset of abnormal involuntary movements. We describe this patient and review the literature on movement disorders and herpes simplex virus encephalitis. Current understanding of the pathophysiology of post-herpes simplex virus encephalitis movement disorders proposes 2 possible mechanisms that may be responsible: reinfection with the resumption of viral replication, or a postinfectious, immune-mediated process.