This report describes the case of a patient who presented with bilateral vitritis that led to a diagnosis of small-cell lung cancer (SCLC). A 70-year-old man was examined due to bilateral gradual visual deterioration. Symmetrical vitritis was observed in both eyes with no evidence of other fundus pathology. The opthalmological diagnosis was bilateral paraneoplastic vitritis. The patient was an active smoker and had a short history of weight loss. A systemic evaluation resulted in a diagnosis of SCLC. The appropriate cancer treatment was provided, as well as a short-term oral steroid. The vitritis responded well to steroid treatment. Ocular manifestations can be an early sign of malignancy, and ophthalmologists should be aware of this possibility.