The clinical features of exercise-induced paroxysmal dystonia (EPD) are delineated in a pedigree including two affected members (both male) showing an autosomal-dominant inheritance trait. Gait analysis using kinematic electromyography during the motor attacks revealed coactivation of antagonistic calf muscles characteristic of dystonia. In the interval, impaired muscular alternation was observed. To characterize further the pathophysiological basis of the condition, ictal and interictal cerebral perfusion SPECT studies using technetium 99m-ethyl cysteinate dimer (ECD) were performed to establish whether cortical hyperactivity indicative of epilepsy is present during the motor attacks and to identify regional changes in the ictal perfusion pattern that could indicate an anatomic structure relevant to the disease. During the motor attacks, decreased ictal perfusion of the frontal cortex was found in both patients. In contrast, increased cerebellar perfusion was observed. The perfusion of the basal ganglia also decreased. No cortical hyperperfusion indicative of an epileptic nature was seen. Cerebellar hyperactivity in connection with prominent frontal hypoactivity has also been described in both the idiopathic and the symptomatic forms of dystonia. Our findings therefore suggest that EPD represents a paroxysmal movement disorder rather than epilepsy. It is concluded that changes in frontal and in cerebellar function are relevant to the pathophysiology of EPD.