A 58-year-old man with primary large cell carcinoma of the lung presented with rapidly progressive, bilateral visual loss. The patient was alert and oriented, had no complaints of headache, and was found to have full ocular motility. The optic disks and fundi appeared normal. No visual pathway lesions or other CNS abnormalities were detected on neuro-imaging. The authors discuss their differential diagnosis, clinical diagnostic approach, and subsequent management of this unusual patient.