To report a case of an orbital mass diagnosed as metastasis from small cell lung cancer and to provide a review of the literature.

A 66-year-old male with a history of diabetes mellitus and hypertension presented with decreased visual acuity and exophthalmos in his left eye. He had been diagnosed with age-related macular degeneration 13 years prior and had a history of pneumonia that was treated for one month. The best corrected visual acuity was hand-motion in the right eye and 0.04 in the left eye. Optic disc swelling and splint hemorrhage of the left eye was observed on fundus examination. The left eye was protruded and eye movement was limited. On orbital magnetic resonance imaging, an irregular mass in the left intraconal space was found. Incisional biopsy was performed, and histopathologic examination revealed a small round tumor. According to the results of immunohistochemical staining, metastatic tumors were suspected. After systemic evaluation, the patient was diagnosed with primary small cell lung cancer with multiple metastases. After 2 months, the visual acuity was hand-motion and proptosis was not resolved.

In patients with orbital masses, the possibility of metastatic tumors should be considered during differential diagnosis and early biopsy should be performed.