question: INTRODUCTION: To describe the reasons for intensive care unit (ICU) admission and to evaluate the outcomes and prognostic factors of patients with primary central nervous system lymphoma (PCNSL) admitted to the ICU. PATIENTS AND METHODS: Retrospective observational cohort study of 101 PCNSL patients admitted to 3 ICUs over a two-decade period. RESULTS: Acute respiratory failure, mainly secondary to aspiration pneumonia and Pneumocystis jirovecii pneumonia, was the leading reason for ICU admission (33%). Aspiration pneumonia was more common in patients with brainstem tumor (67% vs. 0%, p < 0.001), whereas patients with intracranial hypertension were more frequently admitted for coma without seizures (61% vs. 9%, p = 0.004). Hospital and 6-month mortality were 47% and 53%, respectively. In multivariate analysis, admission for coma without seizures (OR 7.28), cancer progression (OR 3.47), mechanical ventilation (OR 6.58) and vasopressors (OR 4.07) were associated with higher 6-month mortality. Karnofsky performance status prior to ICU admission was independently associated with lower 6-month mortality (OR 0.96). DISCUSSION: Six-month survival of PCNSL patients admitted to the ICU appears to be relatively favorable (around 50%) and the presence of PCNSL alone is not a relevant criterion for ICU refusal. Predictive factors of mortality may help clinicians to make optimal triage decisions. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00415-021-10396-x.