INTRODUCTION:Central nervous system (CNS) relapse in diffuse large B-cell lymphoma (DLBCL) is usually fatal. Risk stratification of patients has historically been poorly defined, and CNS prophylaxis with high-dose methotrexate (HDMTX) can be associated with multiple toxicities. The CNS International Prognostic Index (IPI) defines three patient risk groups for CNS disease. The aims of this study were to evaluate the toxicity of HDMTX and describe outcomes in HDMTX and non-HDMTX patients according to the CNS-IPI. METHODS:205 patients diagnosed with DLBCL between 2004 and 2014, initially treated with RCHOP-like chemotherapy and considered for HDMTX CNS prophylaxis were identified by pharmacy records at two teaching hospitals. Patient records were retrospectively reviewed for HDMTX toxicity, CNS-IPI calculation and CNS relapse. RESULTS:28 patients with DLBCL were selected for two doses of HDMTX. Two of 28 patients received only one dose, and three had their second dose reduced due to renal impairment. 28% of patients experienced nephrotoxicity. 24 HDMTX and 122 non-HDMTX patients were evaluable for the CNS-IPI. No significant difference in the CNS-IPI distribution between the two groups was identified (p = 0.695). Five patients had CNS relapse, two who received HDMTX and three who did not. No significant difference in CNS relapse rate was identified between 24 HDMTX patients propensity-matched to 24 non-HDMTX patients. CONCLUSIONS:HDMTX was well-tolerated by patients. Application of the CNS-IPI identifies a different population of candidates for CNS prophylaxis compared to traditional criteria.