Sildenafil has well-known adverse effects of headaches, hypotension, hyperemic nasal congestion, flushing, atrial fibrillation, and changes in pulmonary blood flow. Little is known about the risk of stroke. We report on a 71-year-old patient who suffered from left middle cerebral arterial (MCA) territory infarction 2 hours after taking sildenafil. The patient was left with motor aphasia and right hemiplegia when his condition had stabilized. We suggest that sildenafil should be prescribed with caution to patients who have higher risks of stroke.