Primary central nervous system lymphoma (PCNSL) is defined as the lymphoma effecting only spinal axis and cranium without systemic symptoms. PCNSL is very rare. Hystologic type of lymphoma that arising in the CNS is most commonly B cell lymphoma. In our study we reported a 47 years old female patient with B cell non-hodgkin's lymphoma of CNS with no evidence of lymphoma outside the CNS. There was no evidence of systemic acquired immundeficiency syndrome.