Introduction: Neutrophil-to-lymphocyte ratio (NLR) is one of parameters complete blood cell count (CBC) tests provide and has been reported to be an easily-accessible prognostic marker in aggressive cancer including non-Hodgkin lymphoma (NHL). Primary CNS lymphoma (PCNSL) is an extranodal NHL with highly aggressive features. However, the importance of NLR has never been assessed in PCNSL. Methods: This retrospective study enrolled 62 biopsy-proven patients whose baseline NLR was available and reviewed their medical records to compare high (≥2.0) and low NLR group in terms of clinical characteristics and outcomes. Results: The low NLR group showed significantly better response rates to induction chemotherapy vs the other one (P = .041). With a median follow-up of 41.5 months, the high NLR group revealed significantly worse 3-year overall survival (OS) (42.5 vs 71.2%; P = .031), and 3-year progression-free survival (PFS) (37.3 vs 60.1%; P = .028). In univariable Cox analysis, high NLR at diagnosis was a poor prognostic factor for both 3-year OS (HR, 2.64; 95% CI, 1.06-6.58; P = .038) and 3-year PFS (HR, 2.41; 95% CI, 1.07-5.42; P = .034). However, multivariable analyses adjusting for IELSG score and induction chemotherapy regimen showed no statistical significance albeit high NLR's tendency towards worse 3-year OS (HR, 2.36; 95% CI, 0.84-6.62; P = .102) and worse 3-year PFS (HR, 2.28; 95% CI, 0.93-5.63; P = .073). Keywords: non-Hodgkin lymphoma (NHL); primary CNS lymphoma (PCNSL); prognostic indices