Primary central nervous system lymphoma (PCNSL) is a rare form of non-Hodgkin lymphoma arising within and confined to the central nervous system and, unlike other primary brain tumors, is very responsive to treatment. Aggressive management can lead to prolonged remissions or cures. However, the prognosis at relapse is generally poor with limited therapeutic options; clearly, new strategies are needed for these patients. Radioimmunotherapy has a growing role in the management of systemic non-Hodgkin lymphoma but has not been evaluated in PCNSL. We report here the first patient with PCNSL treated with radioimmunotherapy.