[Difficulty in diagnosing an orbital non-Hodgkin's lymphoma]

History case of a patient treated for a bilateral orbital inflammatory pseudotumor has been rehospitalised for generalised lymphoma, despite the histological features of this tumor which evoked a pseudo-tumor. This error seems to be frequent because of the difficulties for the histological investigation of the tumor. Actually the application of immunohistochemical techniques and the study of immunoglobulin gene DNA rearrangement patterns allows the diagnosis. Often most of the orbital lymphomas, though apparently isolated, represent a localization of a systemic disease. Their treatment consists in either of radiotherapy in low grade malignancy localized cases or in chemotherapy in the others sometimes associated to radiotherapy.