Chemotherapy, with or without radiotherapy, is the mainstay of treatment for primary central nervous system lymphoma (PCNSL). High-dose methotrexate (MTX) is the most effective drug available to treat these lesions, and it is used in doses of 1 to 8 g/m(2), either as a single agent or in combination with other drugs such as corticosteroid agents, cytarabine, procarbazine, vincristine, carmustine, lomustine, thiotepa, cyclophosphamide, temozolomide, and rituximab. To date, an overwhelming number of different regimens in which high-dose MTX is used have been reported. Given the lack of randomized trials, however, the optimal treatment remains controversial. Varying methodology makes the comparison of available studies extremely difficult, yet some common themes can be found throughout the literature. Treatment paradigms vary considerably according to the patient's age. Most studies support the use of chemotherapy-only treatments for elderly patients (> 60 years), given the high risks of neurotoxicity associated with radiotherapy. Nevertheless, the prognosis remains poor regardless of the chemotherapy chosen, and less toxic regimens might be preferable for such elderly patients. Conversely, in younger patients (< 60 years), there is growing evidence that commonly used chemotherapy-only regimens are associated with increased relapse rates that may not justify deferral of radiotherapy. Thus, a significant focus of research has been the development of intensified chemotherapy regimens that could replace radiotherapy. In this article, the authors discuss the principles guiding the use of chemotherapy for PCNSL, and critically review the available literature, including the most recent trials.