Temozolomide is a well-tolerated alkylating agent, that is able to permeate the blood-brain barrier (BBB), and has additive cytotoxicity when given with radiotherapy (RT). A phase II trial assessing temozolomide 150 mg/m(2)/day, for 5 days every 28 days in primary central nervous system (CNS) lymphoma (PCNSL) patients with negative human immunodeficiency virus (HIV) serology, Eastern Cooperative Oncology Group (ECOG) performance status (PS)<4, previously treated with high-dose methotrexate-containing (HD-MTX) chemotherapy and/or RT was started. Twenty-three patients were enrolled. Median age was 60 years. Five complete remissions (median duration 6+ months; range 2-36 months), one partial response, four stable disease (median duration 7.2 months, range 2-16.5 months), and 13 progressions were observed. No major toxicities were observed, apart grade 3 vomiting in a single cycle. Main grade 1-2 toxicities were: 15% nausea, 6% vomiting, 9% fatigue and 9% neurological symptoms. This is the first prospective trial assessing single-agent activity in PCNSL at failure. Although some patients had a poor PS and had been heavily pre-treated, temozolomide yielded 26% objective responses and was well tolerated without any major toxicity.