Primary central nervous system lymphoma (PCNSL) can be misdiagnosed as tumefactive multiple sclerosis (MS ). Both entities share common presentation of focal neurological deficit , radiological enhancement, response to steroid initially and some time relapsing remitting course. Further more , biopsy can be misleading as it may show demyelination features. This is making the diagnosis of PCNSL challenging . So, high index of suspicion and awareness that brain biopsy might show demyelinating changes is needed for earlier diagnosis & management