Motor dysfunction is associated with schizophrenia, and recent longitudinal studies indicatethat it precedes the onset of clinical symptoms. Of particular interest is the heightened occurrenceof involuntary movements, which are apparent as early as infancy and suggest the presence ofsubcortical brain abnormalities. In this article, we present the results of a study of spontaneousmovements in adolescents with schizotypal personality disorder (SPD). SPD is a syndrome thathas been shown to be genetically linked with schizophrenia and is often observed prior to theearly adult onset of schizophrenia. Systematic coding of videotapes of diagnostic interviewsrevealed that the SPD group showed significantly more involuntary movements of the head,trunk, and upper limbs than did normals and adolescents with other personality disorders. Therewere no diagnostic group differences in the rate of voluntary movements. Salivary cortisol,measured before the interview, was positively correlated with involuntary movements. Takentogether, the findings provide further support for the hypothesized etiologic relation betweenSPD and schizophrenia. Based on a neural diathesis-stress model, potential underlyingmechanisms are discussed.