Three months prior to presentation, a 76-year-old woman suffered from insomnia and was prescribed some antidepressants and hypnotics. At that time, brain MRI showed no cerebral infarcts. Having developed an action tremor of the left hand, bradykinesia, and unstable gait, she visited our hospital. Neurological examination revealed rigidity of the neck and left limbs, clumsiness of the left hand, action tremor, and decreasing swing of the left arm while walking. 123I-metaiodobenzylguanidine scintigraphy showed no decrease of the heart/mediastinum ratio. The second MRI showed an old cerebral infarct located just in the right external segment of the globus pallidus. Since drug-induced parkinsonism was suspected, paroxetine and trazodone were discontinued, but her symptoms did not improve. We concluded that her hemiparkinsonism was due to the cerebral infarct in the right external segment of the globus pallidus, because her symptoms did not respond to dopamine agonist and L-dopa therapy, and the onset of symptoms corresponded with the time of appearance of the cerebral infarct. This is a rare case that is important for understanding the mechanism of parkinsonism.