Primary central nervous system (CNS) lymphoma is a rare and aggressive brain tumor with unsatisfactory outcome. However, early diagnosis and treatment can positively affect prognosis. Primary CNS lymphoma occasionally was indistinguishable from demyelinating diseases, such as acute disseminated encephalomyelitis or multiple sclerosis. We present three patients who were misdiagnosed with CNS demyelinating diseases by neuroradiological and pathological studies.