The standard treatment for primary CNS lymphoma (PCNSL) involves high-dose methotrexate-based chemotherapy (HD-MTX) alone or in combination with whole brain radiotherapy (WBRT). The combined modality regimen carries a substantial risk for cognitive impairment, and HD-MTX alone has been used more often recently in part to reduce neurotoxicity. In this study, we assessed cognitive functioning and quality of life in PCNSL survivors treated with WBRT + HD-MTX or HD-MTX alone. Fifty PCNSL patients in disease remission underwent a posttreatment baseline neuropsychological evaluation, and a subset of patients completed a follow-up evaluation. Quality of life and extent of white matter disease and atrophy on MRI were assessed. Comparisons according to treatment type after controlling for age and time since treatment completion showed that patients treated with HD-MTX alone had significantly higher scores on tests of selective attention and memory than patients treated with the combined modality regimen. Patients treated with WBRT + HD-MTX had impairments across most cognitive domains, and these were of sufficient severity to interfere with quality of life, as over 50% were not working due to their illness. Patients treated with HD-MTX alone did not meet criteria for cognitive impairment but scored within 1 SD below the normative sample on most tests. Patients with more extensive white matter disease had lower scores on tests of set-shifting and memory. Cognitive dysfunction was more prevalent in PCNSL survivors treated with WBRT + HD-MTX compared with patients treated with HD-MTX alone.