A 55-year-old man with squamous cell carcinoma of the esophagus had vertical diplopia secondary to metastasis to the brain stem. The lesion was detected by magnetic resonance scanning but not by computed tomography. Clinically, the disturbance in ocular motility localized to the right inferior rectus muscle. At autopsy, a single metastasis was present in the brain stem, contiguous with the right oculomotor nucleus and involving a small portion of the nucleus. The findings in this case support the concept that, in humans, the oculomotor nucleus is organized into functional subnuclei.