Primary central nervous system (CNS) lymphoma (PCNSL) is an uncommon extranodal non-Hodgkin lymphoma often presenting as a single brain lesion within the CNS. On histopathological evaluation of PCNSL a positive CD10, which is frequently observed in systemic diffuse large B-cell lymphoma, is present in approximately 10% of PCNSL. We describe a case of CD10-positive PCNSL presenting with multiple posterior fossa enhancing lesions in an immunocompetent older woman with a history of breast cancer successfully treated by the RTOG 0227 protocol consisting of pre-irradiation chemotherapy with high-dose methotrexate, rituximab, and temozolomide for 6 cycles, followed by low-dose whole-brain radiation and post-irradiation temozolomide.