High-dose Methotrexate (MTX) is the most useful cytotoxic drug used in the treatment of primary central nervous system lymphoma (PCNSL). Dose reduction should be made in patients with reduced renal function. We evaluated the age of patients over a period of 22 years and estimated their glomerular filtration rate. One hundred and two patients were treated in Nottingham University Hospitals (a regional centre for neurosurgery) during the period 1986-2008. Patients were treated either with the BVAM regimen (carmustine, vincristine, cytarabine, MTX) or with CHOD (cyclophosphamide, doxorubicin, vincristine and dexamethasone) given for one cycle prior to BVAM. The age at which patients were diagnosed with PCNSL increased during the period of the study. During the first half of the study period (1986-1997) the median age was 60.5 years, compared to a median age of 65 years during the second half of the study period (1998-2008) (P = 0.001). The estimated glomerular filtration rate decreased with age over 40 years in a similar way to the general population. The increasing age of patients with PCNSL and decreasing renal function limit the intensity of chemotherapy with MTX containing regimens.