Up to 20% of all primary CNS lymphoma (PCNLS) patients are aged 80 years or older, yet data are limited on how best to treat this rapidly growing population. Despite demographic pressures and the proven efficacy of methotrexate (MTX)-based regimens, automatic de-escalation of care based on age is standard practice outside of tertiary care centers. We performed a retrospective review of all PCNSL patients aged 80 years or older treated at Memorial Sloan-Kettering Cancer Center from 1993 to 2011. Demographic and clinical variables were evaluated as predictors of survival by multivariate analysis. Twenty-three of 24 patients were treated with chemotherapy (92% with high-dose MTX, typically in combination with vincristine and procarbazine). One patient received ocular radiation alone for disease limited to the eyes. Response to treatment was noted in 62.5% of patients; 9 (37.5%) had refractory disease. Median overall survival was 7.9 months (95% confidence interval [CI]: 5.8-53), and median progression-free survival was 6.5 months (95% CI: 4.4-29.5). Two-year survival rate was 33%; 3-year survival rate was 17%. Three patients lived more than 4 years postdiagnosis. Most patients tolerated therapy well, and despite low baseline creatinine clearance, no significant renal toxicity was noted. Response status and deep brain involvement were identified as the most important predictors of survival. Multidrug regimens containing high-dose MTX are feasible and efficacious among the oldest patients, particularly those who achieve a complete response by their fifth treatment cycle. Aggressive therapy should be offered to select patients irrespective of advanced age.