Orbital tumor is a rare presentation of lymphoma. Unspecific symptoms, local infiltration, chronic progression may mimic other more common orbital diseases and often make the diagnosis difficult. We report a case of orbital non-Hodgkin lymphoma initially diagnosed as Graves’ disease. A 65-year-old woman was admitted to the Department of Endocrinology with a diagnosis of a left eye tumor. On admission, apart from the tumor, exophthalmos and the upper eyelid proptosis were present. The lesion had been observed for two years before hospitalization. Due to the muscle infiltration, as detected on computed tomography scanning and magnetic resonance imaging, Graves’ disease was suggested. The thyroid function was normal. Further diagnosis performed during hospitalization revealed lymphoplasmacytic lymphoma. Lymphoma may manifest as a localized orbital tumor without extraorbital or constitutive symptoms. Rare orbital diseases, among others lymphoproliferations, should be taken into account in the differential diagnosis of exophthalmos.