The combination of pure motor hemiplegia and horizontal gaze palsy is a rare but identifiable lacunar syndrome. Among horizontal gaze palsies, one-and-a-half syndrome and abducens nerve palsy are reported to be associated with pure motor hemiplegia in pontine lacunar infarction. Although conjugate lateral gaze palsy is also hypothesized, pure motor hemiplegia with conjugate lateral gaze palsy has never been reported. We present a 75-year-old man who showed right hemiparesis and impaired left horizontal conjugate eyeball movement. Both the findings of the brain CT scan and those of the MRI study were consistent with a small infarction in the left midpontine tegmentum. Magnetic resonance angiography revealed no stenotic narrowing of the vertebrobasilar artery. Radiological findings suggested that pure motor hemiplegia with conjugate lateral gaze palsy, in our patient, might have been produced by the occlusion of a single penetrating branch of the basilar artery.