Although dyskinesias may be one of the first behavioral indicators of progressive striatal dysfunction, a mechanism critically implicated in the pathogenesis of psychotic disorders, little is known about the association between striatal structures and abnormal movements in high-risk populations. Thirty participants with a prodromal syndrome were rated for dyskinetic movements and underwent structural magnetic resonance imaging (MRI). Volumes of striatal brain structures were delineated. Elevated hyperkinetic movements were found to be associated with smaller putamen and results were replicated in the antipsychotic naïve portion of the sample. Participants who converted over a twoyear follow-up period showed significantly smaller striatal volumes and a trend towards elevated dyskinetic movements, relative to those who did not convert. Movement abnormalities may reflect a striatal pathology that is present before formal psychosis onset, and potentially reflective of a heightened vulnerability for conversion.