Non-Hodgkin lymphomas (NHL) of the Central Nervous System (CNS) are rare but they nonetheless constitute a clinical, biological and therapeutic problem of great interest. Primary lymphomas of the CNS account for 2% of all malignant lymphomas and for 0.3-1.5% of all intracranial tumors. Surgery and radiotherapy afford only poor control of the disease. The most satisfactory results have been achieved with combination therapy, surgery + radiotherapy + chemotherapy, but the optimal combination has still to be devised. Secondary neuromeningeal involvement affects a fair number of patients with systemic NHL. The symptoms are broadly the same as in CNS NHL and the treatment as problematic. There have recently been suggestions that the onset of CNS NHL may be exacerbated by immunodeficiency states such as occur in patients who have undergone organ transplantation, in autoimmune disease and, still more recently, in the acquired immunodeficiency syndrome (AIDS). The frequency of these tumors is anyway on the increase and a better insight into the disease in essential.