BACKGROUND Primary central nervous system lymphoma (PCNSL) is an uncommon type of brain tumor that has an aggressive disease course. Its outcomes, including factor-related outcomes, are therefore not well established in our country. OBJECTIVE This study aims to investigate the outcome and prognostic factors in PCNSL patients at our institute. METHODS Retrospective study in a single university hospital. METHODS We reviewed consecutive cases of newly diagnosed PCNSL at Prince of Songkla University from 2005 to 2018. The data were collected to evaluate the treatment outcomes and prognostic factors. METHODS The Kaplan-Meier method for survival analysis, and Cox regression for variable analysis. RESULTS Eighty-seven patients met the inclusion criteria. Patients were predominantly male, and their mean age was 58.8 ± 11.2 years. Only four patients were infected with HIV. Motor weakness was the most common presentation, and neuroimaging revealed multiple lesions in 56.3% of patients. The patients were divided into four groups according to treatment modality: palliative treatment, whole-brain radiotherapy (WBRT) alone, chemotherapy (CMT) alone, and combined WBRT and CMT groups. The median overall survival was 7 months. The 1-, 2-, and 5-year survival rates were 29%, 21.5%, and 4.6%, respectively. The age of >60 years was a significant poor prognostic factor. In addition, patients who received combined treatment exhibited the highest survival rate. CONCLUSIONS PCNSL has a low survival rate, even in the present era. Older age is the most substantial factor associated with unfavorable outcomes. The most effective treatment is combined with WBRT and CMT.