Paraneoplastic optic neuropathy (PON) is a very rare condition. In this study, a case of PON is presented, with the first complaint by the patient being painless vision loss in one eye. In the follow-up of our case, optic neuropathy developed in the fellow eye. Electromyography examination performed due to diffuse body pain and motor loss in the left extremity was compatible with peripheral sensorimotor polyneuropathy. Lung biopsy was planned due to the EMG result and lymphadenopathy detection in thorax computed tomography (CT). The biopsy result of the patient was reported as nonspecific hyperplasia. As the patient’s complaints increased, a paraneoplastic antibody panel was requested and CV2 / CRMP5 antibody was found to be positive. Thereupon, as a result of the repeated biopsy, our patient was diagnosed with small cell lung cancer. We think that paraneoplastic optic neuropathy should be considered in the differential diagnosis in patients of advanced age, smokers, painless subacute vision loss, optic disc swelling, and research in this direction should be insisted on, as in our case.