To identify survival predictors and to design a prognostic score useful for distinguishing risk groups in immunocompetent patients with primary CNS lymphomas (PCNSL). The prognostic role of patient-, lymphoma-, and treatment-related variables was analyzed in a multicenter series of 378 PCNSL patients treated at 23 cancer centers from five different countries. Age more than 60 years, performance status (PS) more than 1, elevated lactate dehydrogenase (LDH) serum level, high CSF protein concentration, and involvement of deep regions of the brain (periventricular regions, basal ganglia, brainstem, and/or cerebellum) were significantly and independently associated with a worse survival. These five variables were used to design a prognostic score. Each variable was assigned a value of either 0, if favorable, or 1, if unfavorable. The values were then added together to arrive at a final score, which was tested in 105 assessable patients for which complete data of all five variables were available. The 2-year overall survival (OS) +/- SD was 80% +/- 8%, 48% +/- 7%, and 15% +/- 7% (P =.00001) for patients with zero to one, two to three, and four to five unfavorable features, respectively. The prognostic role of this score was confirmed by limiting analysis to assessable patients treated with high-dose methotrexate-based chemotherapy (2-year OS +/- SD: 85% +/- 8%, 57% +/- 8%, and 24% +/- 11%; P =.0004). Age, PS, LDH serum level, CSF protein concentration, and involvement of deep structures of the brain were independent predictors of survival. A prognostic score including these five parameters seems advisable in distinguishing different risk groups in PCNSL patients. The proposed score and its relevance in therapeutic decision deserve to be validated in further studies.