Primary central nervous system lymphoma (PCNSL) is a relatively uncommon primary brain tumor, but it has become the focus of many clinical trials because of its rising incidence and unique sensitivity to systemic chemotherapeutic agents. Radiotherapy can achieve high response rates and remissions in most patients, but survival is usually only 12-18 months because disease recurs. The addition of systemic chemotherapy, particularly intravenous methotrexate, had markedly improved disease control and many patients can achieve a durable remission and occasionally cure of their disease. Conventional systemic lymphoma drug combinations such as cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) are ineffective. High-dose methotrexate is the single most active and important agent in the treatment of this disease. Whether improved disease control can be accomplished by adding other drugs to high-dose methotrexate or whether it is sufficient as a single agent has yet to be answered. High-dose methotrexate combined with cranial irradiation yields a median survival of at least 40 months and five year survival rates of 22%. However, neurotoxicity is substantial in a significant proportion of patients, particularly those over the age of 60 at the time of treatment. As many as 50% of such patients develop severe dementia. This is particularly important in a disease where approximately half of patients above the age of 60 had presentation. Efforts are now being directed towards not only improving disease control but also minimizing late neurotoxicity. Most efforts are currently directed towards using chemotherapy as the sole modality in the treatment of PCNSL, but both an optimal chemotherapy regimen, and the role of radiotherapy remain to be determined.