A 12-year-old boy presented with persistent proptosis and periorbital swelling after a school altercation. MRI revealed a mass in the right superonasal orbit extending along the orbital roof to the frontal bone and right frontal sinus, and intracranially to the dura of the right frontal lobe. Immunohistochemistry revealed CD20- and CD43-positive B cells consistent with a low-grade B-cell lymphoma. The patient was diagnosed with stage I ocular adnexal MALT lymphoma and treated with radiation therapy, followed by systemic chemotherapy. However, an enhancing orbital and intracranial mass remained on follow-up imaging, leading to a repeat biopsy, which was consistent with a diagnosis of Rosai–Dorfman disease. This is the first reported pediatric case of ocular adnexal MALT lymphoma with subsequent development of Rosai–Dorfman disease.