Although repetitive involuntary movements are a well-recognized manifestation of carotid occlusive disease, similar movements have not been reported with a lacunar infarction outside of the basal ganglia or subthalamic nucleus. We describe a man with tonic spasms associated with a lacunar infarction in the right ventral pons. Involuntary tonic spasms of a paretic limb developed acutely in a 69-year-old hypertensive man with a clinical presentation of pure motor hemiparesis. Magnetic resonance imaging demonstrated a lacunar infarction of the ventral pons. There was no evidence for carotid occlusive disease. An electroencephalogram recorded during the movements showed no abnormality. The abnormal movements responded well to treatment with oral diazepam. A brain stem lacunar infarction may be associated with involuntary tonic limb spasms clinically similar to those reported as paroxysmal symptoms of multiple sclerosis.