Primary central nervous system lymphoma (PCNSL) is a type of non-Hodgkin lymphoma confined to the central nervous system. Its diagnosis requires a stereotactic biopsy, which is an invasive procedure. Cerebrospinal fluid (CSF) analysis is less invasive and easier to perform than a stereotactic biopsy. We hereby report a PCNSL case diagnosed using CSF analysis and treated with systemic chemotherapy.