BACKGROUND. The most effective treatment for a new diagnosis of primary central nervous system lymphoma is high-close methotrexate (MTX)-based chemotherapy followed by whole-brain radiation therapy (WBRT). However, this combined modality treatment carries an increased risk of delayed neurotoxicity. For patients who achieve a complete response (CR) after induction that uses high-dose MTX-based chemotherapy, it is not clear if consolidation treatment is necessary. Therefore, a retrospective study was conducted to assess the impact of consolidation treatment after a CR to initial induction chemotherapy on disease control and survival.