OBJECTIVE: Diabetes mellitus has been implicated as a risk factor for tardive dyskinesia. The authors examined the association between abnormal movements and impaired glucose metabolism, which often precedes the development of overt diabetes, in patients with schizophrenia. METHOD: Twenty-one patients with DSM-IV schizophrenia receiving neuroleptic medication were given oral glucose tolerance tests involving serial glucose and insulin levels. These values were analyzed in relationship to abnormal involuntary movement ratings. RESULTS: Patients with impaired glucose tolerance had higher mean abnormal movement scores than those without glucose intolerance, but this difference was not statistically significant. There was, however, an association between the magnitude of the fasting insulin level and abnormal movements after the authors controlled for fasting glucose level. Additionally, the fasting glucose level predicted abnormal movements after the authors controlled for age. CONCLUSIONS: Hyperinsulinemia and hyperglycemia associated with insulin resistance may potentially contribute to the pathogenesis of tardive dyskinesia. Findings from this small cross-sectional study suggest a possible relationship that requires clarification through larger, longitudinal studies.