There are different etiologies of hemiparkinsonism. A few patients with hemiparkinsonism secondary to infarction in the contralateral substantia nigra have been reported in the literature, and only one of these patients presented with pure hemiparkinsonism. This paper reports the unusual case of a patient presenting with pure hemiparkinsonism secondary to a lacunar stroke in the substania nigra. A 66-year-old man who presented with a 5-year history of left-sided hemiparkinsonism manifested by tremor, rigidity, and bradykinesia located mainly on the upper extremity. Magnetic resonance imaging of the brain revealed a lacunar infarct located in the right substantia nigra. Patients experiencing sudden hemiparkinsonism should be investigated to rule out any abnormality in the contralateral substantia nigra. This case points to the significance of neuroimaging in the evaluation of unilateral parkinsonism.