Primary central nervous system lymphoma (PCNSL) is a rare neoplasm that has captured popular attention because of its rising incidence and marked chemosensitivity. It is a non-Hodgkins B-cell lymphoma (NHL) that appears confined to the central nervous system (CNS) at presentation but may be multifocal within the brain or involve the leptomeninges or eyes at diagnosis. Like systemic lymphoma, it is highly sensitive to corticosteroids, and administration of steroids should be withheld until the diagnosis has been confirmed histologically. Currently, the initial treatment of choice incorporates high-dose methotrexate (HD-MTX) either as a single agent or in combination with other systemic chemotherapies. Whole-brain radiotherapy (WBRT) can be a highly effective treatment modality when combined with MTX, but the combination causes an unacceptably high incidence of severe permanent neurotoxicity, particularly in patients over age 60. Therefore, chemotherapy alone is the initial treatment of choice in older patients. This approach is also being explored in younger patients, but it is possible that deferring radiotherapy may compromise disease control. Consequently, the role of radiotherapy remains to be clarified in newly diagnosed younger patients with PCNSL.