The recurrence of non-Hodgkin lymphoma (NHL) in the central nervous system (CNS) is rapidly fatal in most cases. Highly aggressive lymphomas, such as lymphoblastic and Burkitt lymphomas, carry a high risk of CNS relapse. CNS relapse in intermediately aggressive subtypes, such as diffuse large B-cell lymphoma, is uncommon, but not rare. The risk of CNS relapse in indolent lymphomas is low. Prognostic markers of CNS relapse include elevated serum lactate dehydrogenase levels, the presence of B symptoms, and extranodal involvement at more than one site. Most centers give prophylactic CNS chemotherapy to patients considered at high risk of CNS recurrence. However, definitions of risk factors vary, and there is a lack of consensus regarding prophylaxis indications. More research is needed to define which patients might benefit from CNS prophylaxis at initial treatment and to find the optimal regimen for prophylaxis. A variety of treatments have been used to treat CNS relapse, but current regimens have had little success in extending survival after CNS relapse. Although long-term survival has been reported in a minority of patients with isolated CNS recurrence after treatment with methotrexate, more effective regimens are needed if survival times after relapse are to be prolonged.