Despite intensive research, the mechanisms of action of electroconvulsive therapy (ECT) remain elusive. In addition, there are no known biological factors predicting ECT responsiveness in bipolar patients. A study was conducted to investigate the relationship between ECT responsiveness and tardive dyskinesia (TD), a common side effect of neuroleptic therapy, and its subtypes (i.e., orofacial and limb-axial dyskinesias) in a group of 18 bipolar patients. There was a significant difference in orofacial dyskinesia scores between ECT responders and non-responders (p less than 0.005), while there was no significant association in scores of limb-axial dyskinesia between ECT responders and non-responders. These findings suggest an association between ECT responsiveness and the presence of orofacial dyskinesias in bipolar patients with TD and add further support to the notion that TD is a heterogeneous disorder comprising at least two subtypes with distinct underlying pathophysiological mechanisms.