To report a case of orbital mucosa-associated lymphoid tissue (MALT) lymphoma that occurred in a patient with rheumatoid arthritis (RA).

A 70-year-old male with alleged RA presented with a 3-month history of spontaneous and painless upper and lower eyelid swelling in the right eye. On initial examination, palpable nodules were observed at the right upper and lower eyelids and orbital computed tomography (CT) revealed a contrast-enhancing nodule just inferior to the lacrimal gland, thus an incisional biopsy was performed. The pathological report showed malignant orbital lymphoma (low grade extranodal marginal zone B cell lymphoma of MALT). Since distant metastases were not detected on whole-body CT and positron emission tomography, the patient was advised to keep previous medication and regular follow-up examinations.

The possibility of MALT lymphoma should be considered as a differential diagnosis in patients with eyelid swelling and autoimmune diseases such as RA.